There are two kinds of people when it comes to coaching: those who like to find out what to do, and those who like to be told what to do. Personally, I respond to commands better, so I would ask my coach to straight up tell me what I need to do. Good instructions include things like "You should wall out with fairs more often; it's one of Jiggs' best tools", "You're shield dropping isn't consistent enough; maybe lay off of it this next game", and "Take deep breaths when the going gets rough; you're choking when your percentage gets high". The key here isn't to tell them what they did wrong or right, just tell them what to do.
For a person who likes to thoroughly process their shortcomings, you need to ask them the right questions. For me, that's harder. I'm better at just telling someone what to do (I wonder what that says about me...) as opposed to finagling with questions. But I've heard that this method is easier for certain people. Good questions could be "What can you do to get rid of that ROB's gyro?", "How can you connect with Disable more often?", and even "What do you think went wrong/really well in that last game?" Keep them thinking, it'll distract them from a loss and keep them from getting cocky after a win.
You can actually ask your friends what kind of coach you want to be. If your friend says "Just give it to me straight at the end of each game", do that. If he/she says "talk me through the match and mix in compliments with constructive criticism", do that. Unfortunately, few people will know 100% what they need in a coach. Just work with them over time and you'll work the kinks out.
Depending on how good of friends you are, the professionalism might change. If you're good friends, you won't need to keep it formal (unless they ask you to). This is really a minor point, but one worth mentioning. If your friend isn't taking you seriously, the coach/trainee relationship will strain.
Huge thing: you need to be able to calm down your friend. Everyone gets salty, and that's fine. Just be sure you can keep them in the game zone and out of the rage zone. This is probably one of the hardest things about coaching and it really tests your patience.
Hope this helped.
