Some trappers like to use Oath Shot to recharge their traps after laying down their initial "set." This is, however, too costly for Rangers with low Expertise.
In PvE, foes can be lured to the traps with a bow, but this tends to bring the foes in a haphazard fashion. It is generally beneficial for a group of enemies to arrive on top of the traps simultaneously. To do this effectively the "puller" will have to aggro the mobs, then run them to the traps in clumps. There are several techniques for clumping foes - running circles around them and using a stuttered run are the popular methods.
Once they activate the traps, monsters will scatter quickly if not killed outright by the traps set. Therefore it is advisable to bring traps that immobilize mobs. Barbed Trap (or Snare with Tripwire) are great, although most farming trappers use Spike Trap.