unfortunately, guardians aren't the smashy type :|
my advice for guardian: stand around and cast buffs until stuff dies?
actually, I have no idea how Guardian plays. But Kell, are you asking how to level in general, or how to spec your guardian as you level? I wouldn't worry too much about speccing, as most people should be able to find any play style they like with their class. I've heard people say that guardian is great for fire/condition damage, but I'm sure there's other routes to go. Damage probably isn't that great, but Guardians have, I think, unequaled use in party support and overall survivability. My thought as a guardian would be to try and make myself that best type of support/tanky class I can be.