This is a good question, but a hard one to answer. There are a lot of challenges for young riders to try and break into the professional ranks. Luckily in the US, our federation is working very hard to bridge the gap, and to encourage the U25 and developing professional divisions.
I think the best advice is to ally yourself with respectable professionals and to open yourself to the opportunity of learning all aspects of the sport.
Put yourself out there, try to work with the best, and keep your focus on your goals. I've learned that the harder you work, the luckier you get!!