Start figuring out who is going to write your recommendation letters as soon as possible. I found these letters to be the biggest hold up. As soon as I thought they were sent out, programs would lose them or say they never got them, which resulted in another 2 week delay.
Ask for them in April so that you can have your file completed at programs by mid-June. This may seem early, however, I know of one program (UCLA's anesthesia-based program) that started to interview in July! However, with most programs you will be OK if your file is complete by late July.
Gather your supporting documents (board scores, ITE scores, personal statement, update your CV, medical school transcripts, medical school diploma, state license if you have it etc.) and print off the applications from the respective websites. Most of the interviews will be sept/oct/nov.
Be sure to schedule rotations that will allow you to be off for interviews during those times. A LOT of CA-3s make the mistake of not planning for time away for interviews during these months.
I think this thread is great, however, I wish we could get even more fellowship reviews going. Despite the good quality of this forum, I found that there was VERY little information available on-line about each program and it made showing up for an interview almost mandatory to find out which programs were the best (for me). Keep on posting!