First year: If you are planning on going into academic medicine, research may help. Otherwise, IMO, there is not much you can do besides honor your classes. People will say pre-clinical grades do not matter. But, when it comes down to junior or senior AOA, it will matter at most schools. If you are interested in one field, I would shadow a doc (both in the community and academic setting) to see how you like it. Go visit the ENTs in clinic if you are interested in ENT. It will only help later on - they will know you. It makes a big difference.
Second year: Obviously ace the board. If you are planning to apply through SFMATCH for nsurg, neuro, ophtho, ent, or plastics, plan your third year well - try to have all your rotations in the field done by july, august of your third year. You don't want to be waiting for a letter of rec in September of your senior year with the sfmatch.
Third year: move anything you are NOT interested in to fourth year. However, most schools will not allow you to move core clerkships like medicine, surgery, pediatrics. Other clerkships may be less demanding. I would try to schedule your field of interest late in your third year if you are pretty confident about entering the field. If you are unsure, I would try to schedule it in the middle of your third year. Since you want to get back to CA, I would suggest doing an AI there (unless your school has a reputation of sending students out to CA). However, you better be a star player during your AI - IMO, it is so much easier to make one mistake during the month than to look like a star.
Fourth year: not much will matter except for your AI ... oh, and passing step two.
