Your absolute best bet is going to be finding a decent instructor (not a coach, although they can be the same person, it isn't often you find both in one entity) and getting stroke instruction. Swimming is a very form intensive sport, to where correct form has a significant impact on both competitive times and on longevity. Bad form can easily wreck shoulders and cause other injuries.
Another good resource, oddly enough, is youtube. There are quite a few good instructional videos on there, and I also recommend a virtual instruction site such as Finding Freestyle.
You may also hear recommendations for Total Immersion, which I don't find to be a bad system for teaching beginners to be comfortable in the water, with a basic stroke that functions decently. My main contention is that I don't find it teaches a very fast style of swimming, it teaches you to complete, rather than compete the swim. However, there are some individuals that have used the system and are quite speedy, so it may work for you as well.