Just hit lvl 80 and need some guidance.
Go to http://gw2buildcraft.com/calculator/guardian/ and play around the site until you get a build you like.
You can switch gears until you’re content with a decent health and defense to not get 1 hit downed, and getting a good balance on power, crit chance and damage.
If you’re just starting out and you’re inexperienced, I suggest taking full Soldier set/trinkets, Ruby or Beryl gems and any damage Rune.
You’ll have high amounts of defense, health and power, but low crit chance and crit damage.
Your gear will allow you to survive pretty long while you figure fight mechanics, tricks and such.
After you’re pretty experienced with it, you can run full Berserk or a mix of Berserk and Soldier/Knights for better damage.