What he said. One to note is that some programs take part in VSAS while others don't, so do your research early. It's hard to get away rotations during 4th year before September, so make sure you don't start in March like I did.
As far as audition rotations go, people's opinions differ about it. My opinion is that you should go for it unless your program has a well-known ophthalmology department. If you don't come from a school with a national reputation, you'll gain more than lose doing an away rotation. One of my regrets was that I did not do more away rotations. Some attendings may say that it does no good, or can do more harm than good, and it's true. However, keep in mind that the advice some attendings give were the same tidbits of advice they gave 6-7 years ago, and they also don't realize how much has changed since then (and how untrue some of their assertions are as well). On interviews, I had some attendings unaware that the average Step I score for ophtho applicants is in the upper 230s, and that they are so many qualified applicants these days they all run together and need some personal connection to applicants (hence: away rotation). Just my 2 cents, being on both sides of the experience.