Once you hit lv 30, your build is pretty much complete and you don't have to lv up any more. You still can lv up if you want..but very slowly, and your character wont improve that much. It's called a "soft cap".
Some ppl grind and grind to get heirlooms, but those aren't THAT much better than normal weapons...so its not necessary if you don't want to lv up more and more.
Just get to around lv 30 and enjoy your peak performance! Any character above lv 30, gen 1 is not so significantly better than other players that a player's skill cannot easily overcome the gen/level difference.