It seems most of us that ulitimately matched ortho came in wanting to do it. You've received great advice from the other posters. Here's my two cents:
1) Doing well in pre-clinicals and really learning the material well will make reviewing/studying for boards and doing well on them a whole lot easier. Board studying is a time when you want to review, not learn, the material.
2) Keep an open mind in third year. It's good to have a goal of what you want to do, but don't keep the blinders on the whole year. Try to learn something on every rotation that can mold the way you practice later in your career. Watch how different attendings interact with their patients. Think about other specialties and move them around on your list based on pros/cons. For instance, I hated IM because of dealing with lazy adults who don't want to get better and instead just want to complain about their chffromhypertensionneuropathiesandkidneyfailurefromdiabetescopdfromsmoking, all diseases they could've prevented years ago. But I really enjoyed my peds rotation because kids want to get better for the most part and you can usually make them laugh and forget they are at the doctors about to get poked with a needle. So now I'm considering a peds fellowship because of that.
3) When you are on surgery rotations, pay attention to the procedures they do most often. Those will be the bread and butter that you will probably spend most of your career doing. Remember that rotating at a residency program and rotating with a community PP doc will be completely different based on variety of cases.
4) Research sucks IMO. I didn't do too much (1 paper, 1 chapter for an online e-book). I don't plan on doing research during my career other than residency. Just mark the box off on the checklist and move on.
5) Aways in 4th year are important, not just to show yourself off to other programs but to also so you can see what your top programs are really like on a day to day basis.
6) Enjoy med school. It will fly by. Just remember to take it one day at a time and not get too far ahead of yourself. Also no matter how bad the suck is, they can't stop time. You will get through it.