You will need a Torque Bow and a Sniper for this one.
When you first meet Raam, take the cover that is in front of you.
He will normally send his kryll at you, so once he does this, shoot him with the Torque Bow, get out your Sniper, and shoot him in the head (make sure you aim for him in the head with both weapons, that is his weakest point, and always get the active reload).
Continue this process. if you run out of ammo, you then have two options:
If he goes up the middle, blind throw a grenade.
If he goes to the sides, roadie run to the other side (when he is close to you), and there is a troika with your name on it. Blast him to bits!