From the perspective of this Shliach Tzibur:
1. Keep it down. It's nice to shrei and yell and daven real loud, but pipe down once the Shliach Tzibur (the guy leading the service) starts to say his part. No Chazan should have to yell and scream over the cacophony to be heard. It's just plain rude to keep yelling out your personal davening at the expense of the tzibur. Especially if you are several prayers behind.
2. Make a designated "Emes". Every minyan should assign one person to be the last "Emes" at the end of the Shma. Ideally, this should be the Rabbi of that congregation. Nobody needs to be frummer than the Rabbi. When he says his Emes, then the Chazan can say his and the service should proceed. There is no need for the competition to be the last one. As far as I'm concerned, anyone who shleps out their kriyas shma in an attempt to be "the last man standing" is just being chutzpadik to the Rav. If you really are that slow, that's fine; there's nothing wrong with it. Just keep it to yourself and don't try to be louder than everyone else. And if you're one of those guys who puts in a 30 second pause between Shma and Ve'ahavta (yes, I've been counting) in order to artificially prolong your prayer, then it's MY time that you're wasting there, and I will not be waiting for YOU to finish.
3. Synchronize your Kaddish. Maybe it's my musical background, but I really do think that it's possible to both say Kaddish aloud and listen to the other mourners at the same time so that you say Kaddish together. Nothing irritates me more than one guy who tries to go much faster than everyone else (maybe so he can get all the Amens for himself) or somebody who goes deliberately slower than the rest. Say it rhythmically and together. If you can't hear what the other guys are doing, go stand closer to one of them. And if you're that guy who just can't keep a beat, slowing down and speeding up and putting in bizarre, awkward pauses (imagine William Shatner saying Kaddish), then for goodness sake try to be quiet at least!
That is all.