Put him in Dust Uni.

Tell him this;- pick one weapon and one dropsuit and focus on that. Doesn't even matter if he is good at it. Once he plays with that all the time, he will automatically get good if he has some skills.

If not he is better of playing Tetris

I'd say, next to basic FPS skills, map awareness and playing your role are the most important parts to learn. Unless you use the vanilla AR assault, there is a lot of tactics and techniques that come either through trial and error or explicit explanation of how to act under different conditions.

These are hard to put in writing. They are best learned through a type of 'lessons learned' approach to fighting, failing, and restarting.