Avoid the brakes unless absolutely necessary. As mentioned upthread, you can drift a bit to the side and catch a little wind to moderate your speed, but the main thing is to be looking up the road and anticipate any movements from 5, 10, 15 riders in front. What I was taught when first started riding in groups is to look at the jersey pockets of the rider in front of you and from there scan up the road. You should also be tuned into sounds of freewheeling rather than pedaling. That will often be your first sign.