Depending on your academic calendar, the timing of your application and your options may change. As an SGU student, I will speak about our problems specifically.
Students that begin in August have a good chance to apply for a second year spot at the end of their first year. Most schools begin accepting applications in February march, interview in June, and accept at the end of June/July for an August start date. Having completed only a year of medical school, you likely have had little time to explore research and develop strong relationships with the faculty that may write your recommendations. The school does not have much to use when considering you. They have your first year grades (mostly useful in comparing you to your classmates) and your MCAT scores. Know that you will be competing against people with a 4.0 and a 30+ MCAT. If you can get a hold of someone that has successfully transferred into the second year, ask them who wrote their recommendations. There is a good chance that this person has a reputation for endorsing strong students.
If you are planning on applying for a third year spot at the end of your second year, you will find this to be much harder. Most schools will want to see your USMLE Step 1 score when considering your application. Any January students from the term ahead of you will have already taken their Step 1 and have scores in hand. It will be very hard to compete against someone that already has a 99 even if you end up with a similar score. You can still apply for a third year spot at the end of your third year (which means repeating a year of clinical work). If you decide to do this, know that it will not be enough that you are “so far ahead” of the other applicants in terms of experience, the school will want to see that you have Honors in your clerkships.
Students that begin in January have more options. As a January student, I had the option of applying for a second year spot halfway through my second year. In this way, you have the opportunity to demonstrate A-level work on the second year material that you would have to repeat, you have a little more time to develop relationships with the faculty in hopes of having a strong letter of recommendation written, and you have enough time to become involved in research or other projects that might set your application apart.
You are also well positioned to apply for a third year spot at the end of your second year. Finishing in December, you will have five months off until you begin your clinical rotations. You can use this time to prepare as much as you need to for the USMLE Step 1, you have time to receive your scores and submit them by April (two months before the application deadlines), and you have plenty of time to make sure that your essays, recommendations, and transcripts are heading in the right directions. You also have an opportunity to pursue research or some other project to strengthen your application. The drawback is that you will have to begin your clinical rotations before the interviews begin. This means moving to a new area, finding a place to live, and taking time off to interview. I went through this and recommend starting your rotations instead of deferring them (if you defer, you may have some difficult questions to answer in the interview), subletting an apartment for two months instead of committing to a lease that you may have to break (and leaving any roommates in a difficult situation), and giving ample notice to your site director that you may need to take some time off for interviewing.