If you haven’t started playing yet, you may want to try your hand at it solo before playing in a group with other players. GW1 plays vastly different to what GW2 does. As such, build conventions and much of the game’s mechanics do not work the same way.
If you’re going to start in Prophecies, it may be worth considering leveling up to 20 in Pre-Searing Ascalon, as that will give you a unique title which you can add to your Hall of Monuments. It’s one heck of a grind getting there, but it’s something to consider.
You’ll also want to pick up Eye of the North ASAP, as you’ll need it for your Hall of Monuments, which gives you some fairly nice rewards for GW2.