After experiencing lots of crashes in races and out riding in fast moving racing training bunches like Melbourne's "North Road Ride" this year and I thought I'd pass on this simple advice:
Always ride close to the front of the bunch:
Most accidents happen in the middle or to the rear of the bunch. To stay out of trouble always move as close to the front as you can. Usually the most experienced riders ride at the front so you are usually riding with guys that know how to handle a bike.
Ride on the left or the right hand side of the bunch:
Avoid the middle of the bunch. Probably the most sheltered but also fraught with danger. The idea is not to get boxed in and have nowhere to go. Most accidents happen to cyclists that ride in the middle because they get closed down or are over lapping wheels (see below). Also, if a cyclists sits in the middle and a fall happens in front of them then they have nowhere to go. If you are on the road then sit on the right or left hand side of the bunch. You'll then have an escape route if something happens. The right (furthest from the curb) is better as long as you stay in your lane and don't ride into the passing or on coming cars! The left hand side (closest to the curb) sometimes has fewer options and more chance of being boxed in. NOTE: If you ride on the left you also have to watch that the edge of the road doesn't run out on you!
Avoid crazy riders:
Yep, those are the ones that want to hit the breaks hard when something happens, dangerously overlap wheels or try to ride through gaps that aren't really there. Usually they are riding in the middle or down the back. Or they are trying to zoom up on the inside of the bunch. If you ride up the front then you usually stay away from them anyway.
Don't overlap wheels:
This is an accident waiting to happen. If you are overlapping wheels then you only need the rider in front of you to move across and he/she will take out your front wheel. If you are on the right or the left of the bunch then you might have somewhere to go but if you are riding in the middle of the bunch you'll have nowhere to go. This is something that you will almost never recover from. You will go down and bring a whole lot of riders down with you. In cross wind situations, when you are all strung out it's a little different. But, in big bunches there is no need to do it at all! Especially if you are riding in the middle of the bunch. There is no need to put yourself and your fellow riders in danger.