If you are doing a crit or a circuit race make mental notes where natural places are that will allow movement. For a RR this is more difficult but you also have climbs or times when things get strung out a bit.
It's best to follow a wheel to the front but not always a possibility. Learn to move people as WR suggested. Also a gentle hand on the hip of a rider next to you can safely get you a few inches.
Surfing to the front through the middle is a skill and one I practice still, especially in the early season, to sharpen the spidey senses.