Wow, actually some good insight today. For the youth ages:
Peewee and above: drop him at the rink and go do your shopping, return when practice is over. No need to talk to coach unless you run into him after a game or practice. Do not talk about playing time or coaching style. By this age, you should have done your homework and known what you were getting into. Coaches don't change over the summer. Engage the coach only if your son is having a problem with another kid, and only if your kid can't handle this situation on his own.
Squirt: Squirt minor you're probably still tying his skates, so you get much more exposure to coaches before and after practices/games. Talk to coaches about non-hockey stuff as much as you want, but not just because you're trying to impress him. Just be a normal human being. If you have a hockey issue (playing time - should be about even at this age, skill development, player's attitude) make a phone call and schedule a face-to-face meeting after practice one night to discuss. Don't talk about this stuff in front of other parents, it makes the coach uncomfortable. Don't ever, ever talk about another kid...in front of others or in a private meeting with coach. Squirt major you should be in the locker room less often as the kids start to tie their own skates. By end of squirt major you should be just about where peewees are.
Mite: Just about the same as squirt minor, but the intensity should be ratcheted way down and the bar for calling a meeting with coach should be way higher. At mites, you should probably only check in with the coach a couple times a season to see how your son is getting along with his teammates, whether he is giving consistent effort, and ask whether he is improving his skills and attitude.
My $0.02. I prefer to let him build his own reputation and try to deal with issues on his own. I'd hate to interfere with his hockey experience by being a needy parent, so I err on the side of doing my own thing while he does his thing.
One thing I would recommend at all levels (club hockey) is a short discussion with the coach in January or February to find out where he stands for next year, especially if you are the type that can't make a realistic evaluation of where your own kid fits in with the team. If the coach hasn't approached you by mid-February about next year, then you owe it to your kid to initiate this discussion yourself. This gives you time to work the phones if you need to find another team and possibly get a couple of skates in with the other team before tryouts.
Even simpler. Don't talk to the coach.
Some advice: your kid is not as good as you think he is.