Well I dinged 80 last night and thought I'd write a few tips on levelling and other things I've discovered so far, in case it helps anyone.
EVENTS
(1) The #1 best way to earn xps is events. Always go to them whenever you see one pop up on your map. If not enough players are there yet, be patient and do some stuff in the area and perhaps see if you can start the ball rolling (unless it's a Champion mob, don't try solo'ing those). If people see you active in the area they will probably join in and it soon gains momentum.
(2) Many events kick off chains of other events. Once one event finishes, hang around in the area for a minute or two as often another will trigger. Listen to the NPCs as their chat often hints as to what to expect. Sometimes it pays to follow certain NPCs as they move off and start a new event nearby.
(3) You can kick off certain events yourself by talking to NPCs that have like a circular orange starburst symbol above their heads (and on the map). Also you will often come across events in a suspended state because the NPC running them died. They can usually be revived and the event will continue.
(4) Some events and event chain repeat quite frequently. If you're in a grinding mood it can be a good source of xps and always ALWAYS a better source of xps than just grinding mobs. Grinding mobs is almost never worth it for xps, only reason would be to try and farm drops but even then you'd be much better off doing this within a repeatable event.
PERSONAL STORY
1) Your story quests are a massive source of xps, don't neglect them. They are however usually pretty tough, or they were for Engineer anyway. Definitely don't attempt to complete them when they are higher level than you. No point waiting until you outlevel them though, because you get busted down to the level of the story quest anyway.
2) The story quests 40+ become pretty epic. Some of them take a fair chunk of time to complete, but they are always worth it because the gameplay is wonderful and the xp rewards are usually very good.
3) Your decisions matter, really they do. I had a real kick in the stomach from one decision I made and it really made me think about what I'd caused to happen. Clever stuff.
KARMA, SKILL AND TRAIT POINTS
1) Save your Karma Points. You'll need them for certain types of gear at 80 and you'll need LOTS. Best way to earn Karma is events and WvW. Don't waste your karma points on gear while levelling, you can usually buy similar on the Trading Post for very little.
2) Don't neglect your traits, they have a major influence on your character. Spend your points as you get them, theres nothing to be gained by saving them. Traits also boost stats, so even if you don't have the 5 points you need for the next special ability, still spend them. You gain a free trait respec each time you buy a new manual and the respec costs are relatively small if you make a mistake.
3) You can change the major traits (the ones you choose at 10, 20 and 30 points in a line) at any time without cost. So whilst you can't re-allocate points between the different lines without a respec, you can change your skills within a line for free and try out different ideas.
4) Spend your skills points unless you're saving up for a more expensive skill. You can't respec skills. But don't worry, by 80 you'll have earned almost all the skills anyway and there's enough skill challenges in the game to unlock every skill.
5) Speaking of skill challenges, some of these can be tough solo if your class can't solo veteran mobs. But there's very often other players waiting in the wings or levelling nearby who will leap in if you start the challenge. Because it shows as an event on the map, people often jump in without realising anyway. So just get stuck in!
6) Skills with a red circle on their icon are special racial skills. Some of these are rather nice, depending on your race of course.
CRAFTING
1) Crafting is mostly a waste of time during the levelling process. It EATS mats like you won't believe and unless you spend a lot of time specifically gathering mats you will never be able to have your crafting keep up with your level, meaning you can't make anything useful. Because so many people are power levelling crafting, you can pick up stuff on the Trading Post dirt cheap.
2) Crafting is however good xps. So if you are happy to do all the gathering needed you'll get some good xps from the crafting process.
3) Even if you don't plan to craft gather gather gather. You can either supply crafters with mats to make you stuff, or sell the mats on the Trading Post, or save them for later in case you do decide to craft later.
MONEY
1) make sure to collect the payments you receive for heart completion. If you check your email you'll find NPCs have been emailing you when you complete a heart for them and usually there is coin attached. Lots of people miss this.
2) Farm events. Events give a little coin, the main reason to farm them is for the drops. In events AOE is king because the more mobs you can damage and tag, the more loot you get. All classes get some form of AOE, some better than others of course. But always good to use it in an event, as long as you can handle the threat!
3) If you don't plan to craft (see above) then sell the mats on the Trading Post for profit. Tier 1 mats (copper, jute, rawhide, green wood) all sell well. Tier 2 less well. Tier 3+ better.
4) Sell what you can on the Trading Post. I check every drop I get on the TP but if the price is too similar to the vendor price I just vendor it. You soon get a feel for what sells and what doesn't.
5) Vendoring white items can often be better than salvaging. Usually these return only a small amount of mats, yet they vendor for a fair price.
GEAR
1) Keep your gear upgraded. I found that Masterwork (green) gear is the best bang for buck when levelling because you can upgrade it often cheaply, whereas Rares you feel are more of an investment and tend to hang on to them longer than you really should. That said, I'd recommend getting a rare for your most used weapon type, it does make a difference.
2) You can recover sigils from weapons and runes from armour using certain salvage kits. The blue kits give you a 40% chance of recovering a rune. Black Lion chests have a chance to contain special Black Lion Salvage kits which give you a 100% chance to recover the sigil / rune. This can be very useful if you have a Major Sigil or rune you like the effect of - you can recover it and reuse it, or sell it on the TP for good silver.
3) You can overwrite the sigils and runes in gear by slotting a new one. Some sigils you can pick up cheaply on TP, others you can recover via salvaging (see above).
4) If you like the appearance of a certain piece of armour or weapon, you can use the special transmute stones to copy this appearance onto other items. You get these transmutation stones as quest rewards, from zone completion and in Black Lion chests.
5) Common dyes are dirt cheap currently because there's a suplus. I have a hunch they are going to nerf the drop rates of dyes, so stock up on your favourite colours while you can. The rarer dyes sell well on the Trading Post and if you get some Black or Abyss dye you're onto a winner. Never dropped for me yet sadly.
ZONES
1) There's way more zones in the game than are needed to get to level 80. I reached level 80 with only about 35% world completion. I'd estimate that I gained perhaps 10 levels of the 80 from WvW and crafting, to give you some idea.
2) Remember that you aren't tied to your racial starting zone. If you can find your way to Lion's Arch (via your racial capital city) you can go and level in other racial zones if you wish. Obviously you probably want to stick to your racial start zone for aesthetic reasons, but if there's not many events kicking off then head for Asura, Charr and Human zones as these 3 are the most populated.
3) Zone completion bonuses are nice as you get some xps, some nice coin and a few items. However, as you progress up the levels the rewards from this start to get underwhelming. Definitely worth doing for your first zone or two, after that you may find it better to keep moving on rather than doggedly completing everything in a zone. Completionists can return at 80.
4) If you want to travel large distances on the map as cheaply as possible, use Lion's Arch as a stepping stone. For example, if want to get back to your home city at higher levels you can port to a waypoint just outside Lion's Arch, then zone into the city and use an Asura gate to your city. This is usually cheaper than using a direct waypoint.
WvW and sPvP
1) Don't ignore WvW during levelling as it's great fun and you get some nice xps and karma while you're doing it. You get boosted to 80 and can be surprisingly competitive at lower levels as long as you have a few skills and traits. Level 15 is a good time to start I'd say.
2) The best xps and karma in WvW come from defence bonuses and from capturing keeps. Whilst roaming around killing other players is good fun, if you're there for the xps / karma then look for the seige situations.
3) There are PVE objectives in the WvW zones. Vistas, POIs, skills challenges. Also there are PVE events too. All are worth doing as they reward better xps and loot than PVE zones, but as always if PVE'ing in a PvP zone expect to get ganked from time to time. That said, most players seem to stick to zerging and because the maps are pretty huge you can usually run around unmolested. Just equip some skill that gives you speed boost.
4) PVE gear does influence your power in WvW. So if you want to survive better in WvW wear some gear that boosts toughness and vitality. Glass Cannon builds usually aren't a good idea in WvW.
5) I've had more success with the WvW queue by trying to enter the WvW zones directly via the Asura gates in Lion's Arch rather than using the queuing system on the B button. You still enter a queue but it seems to actually work. If you want to try this, make sure you aren't in Lion's Arch overflow. Also, I've seen it said that cutscenes can pop you out of the WvW queue, so avoid story missions and vistas while waiting, but can't verify this.
6) Structured PvP (sPvP) does not earn you any xps but you can do it at ANY time and it's more fun than you probably expect it will be. Think of it like a mix of WoW Battlegrounds and Arena, but you play only for rank, cosmetics and prestige, not for ever more powerful gear. You are automatically boosted to 80 and will have full access to skills and traits and gear to put you on an equal footing. After that you earn glory points to spend on gear, but this only improves your appearance, never your power. It's always a level playing field based on skill (and class imbalances, hehe).
COMBAT
1) Unlock all your class weapon abilities. To see what weapons your class can use, open your Hero window (H) and check the weapon skills.
2) Don't forget to use both your weapon load outs once you gain them. A lot of classes seem built for weapon swapping. In fact many weapons have sigils which cause effects when swapped to. Engineers and Elementalists can't do this, but they have ways to swap kits or attunements in combat.
3) Learn about combo fields. Certain abilities you and other players have can provide pretty spectacular boosts if used together. For example, firing arrows through a poison cloud creates poison arrows. There's lots and lots of these and I've only worked out a few. In chaotic events mostly they happen by accident, but in smaller scale fights you can often manipulate combo fields better.
GENERAL
1) Explore explore explore! There's some wonderful things to discover, often in the most unusual of places. Not everything is about xps and loot. There's some stuff in the game that just makes you go "WOW" and it's worth poking around in the corners as they planted lots of easter eggs to find. I can't stress this enough, make sure to explore, the game is about more than the quests and combat. There's some great sights and NPC dialogues to be had away from the action. The attention to detail in the game is rather special.
Hope this helps. Have fun!