The rules for this year are much the same as those for second year. You should be volunteering , working in research labs , and focusing on keeping your grades high. Also, if you haven't written the MCAT , or did not preform well the first time, you should be writing it this summer. In my opinion, this is the prime time for a first application attempt.
Many schools like to select candidates the second time they apply.
If you apply for the first time now, then your second application can occur during fourth year. Remember, that applications will be due between October and December of the year in question.