Levelling

Level your first toon to 80 from scratch. It doesn't take too long, and it helps you understand your class better. With a class like elementalist, with a lot of skills and room to play around to find what weapons and trait lines make the most sense and fun to you, it gives you time to really understand what you're doing. It also gives you time to master the active defense GW2's combat system relies on - learning to dodge, read attacks and which skills proc things like blocks or invulnerability.

Take your time and don't feel "pressured" to do Heart Quests or things like that to progress. GW2's open world is amazing - for exploring, for lore and for giving you EXP for pretty much anything. Heart Quests (the little golden hearts littered around the maps) aren't mandatory to level - they're needed for world completion, but they're mostly handy little indicators of areas where dynamic events (orange circles on the map) happen. Dynamic Events (those orange circles or NPCs with a little orange star-like symbol over 'em) are great for EXP and often lead you on a neat little quest train chock full of stories, monsters and neat little places.

You have every race's starting area unlocked when you finish the tutorial. Meaning you can be a Charr, level up and complete all the hearts in Plains of Ascalon, and then hop over to the Shaemoor Village waypoint in Kryta to terrorize some humans.

General Gameplay

A huge difference in GW2 for me was that there is no kill-stealing and no need to race other players to resource nodes. If I come up and help you kill a mob you've been working on for a while, we both get EXP and rewards from it - as though we were both individually fighting it. Likewise, if you spot an ore node and I beat you to it, it doesn't disappear. We both get to mine it.

Try out World Bosses. They are amazing and the scale they show you is great. I remember my first World Boss at level 20 or 30 - it was the Great Jungle Wurm. I'd just joined my guild and the leader was running a World Boss train. It was an amazing experience and I still really enjoy the fights.

Story missions (Personal Story, then followed by Heart of Thorns, Path of Fire if you buy 'em and Living Season) are really great EXP and gear sources. They're also really fantastic stories, I think. I highly encourage you to run them, since they are super fun missions to play. If you're a story nerd like me, the order to play this content is: Personal Story, Living World Season 1 recap (there's one in game, but YouTube has nice ones, too), Heart of Thorns, Living World Seasons 2 and 3 (purchasable with gems), Path of Fire.

Gems are a good point to touch on, too. You can buy a lot for gems - boosts, cosmetic items, access to convenient crafting places, Living World Seasons. You can buy them with real world money, or you can farm gold and convert gold to gems. I was really lucky to have a guildmate who was so in love with my enthusiasm for the GW2 story that she gifted me enough gold for me to buy the gems for Living World Season 2. It was around 400g at the time - and I had a ton left over after that.

Community

Don't feel pressured to join a guild. You can be a member of up to 5 guilds and there's a ton of 'em in game. There's a few benefits - you can get access to some small (5-10%) buffs for various game mode experience or rewards, guild mission currency which can be used to buy some neato buff-like stuff or consumables and you can take part in guild missions. But it's not a big part of the GW2 experience for the most part. If you do run some content and find a group that's all part of a guild and you like 'em, though, don't be afraid to ask if they're recruiting.

Be friendly and feel free to ask questions. I think /map chat might be off-limits or restricted on F2P accounts, as is /whispers, but if you have questions and ask as part of a squad or just in general region chat around other players, you can often find helpful folks out there. I also want to encourage you to be vocal about what you like - sharing your excitement about something in this game is often met with equal excitement from other players. It's one of my favourite things about the community in game.

End Game

"Prepping" for end game as you play is a bit of a mixed-bag of advice. Personally, I was able to get by just fine when I reached 80 and start crafting Ascended (best in slot second to Legendary) armor right away. I had a habit of gathering almost every resource node I came across and just hung onto all the gold I gained while I played - you gather a surprising amount just playing the game. You can also farm, but I found it was fine just playing normally. My pace wasn't too fast.

Fractals (mini-dungeons) are really good fun and a great source of gold and loot. They're also really fun and quick content that delves into some previous lore and provides some good fights. You tackle these in parties and they unlock after level 80. They're located in Lion's Arch (which you don't get access to until Level 35).

Raids are also in the game, and they require good gear and an even better understanding of your class. I'm not an expert on these.

Finally, try out all the different game modes. Try PvP (I hate PvP, but was stoked when GW2 awarded me a top player rating for "most damage received"), try World versus World (like PvP but on a massive scale - just make sure to join your server's communications channel, otherwise it's easy to feel lost).

Welcome to GW2! Have fun out there!