If you are lucky enough to get in a challenge mode team a few tips.
-Rangers don't do the damage hunters do so hold off on the heavy attacks. A simple light attack causes the stun a HU needs to get his/her attacks to connect. Heavy attacks just repulse the enemies making it harder for a HU to attack the enemy.
-The ranger should see which grunt monsters are targeting their HUs and focus on stunning them while the HU finishes them off. Remember light attacks, heavy attacks cause knockback which can throw a HU off balance. and annoy the crap out of the Hu.
-Rangers are also great for detonating player traps quickly. Without a handgun or tech to detonate a player trap, it takes some time for it to explode, which in that time the monsters move out of position or cause you damage.