Hello!
First of all, which college are you planning on attending next year?
I'm a freshman at UMBC (Class of 08). I decided that I wanted to apply to College Park last minute last year (very dull of me) and as expected, I didn't get in for freshman year. I am currently in my Spring Semester at UMBC and I applied for Fall 2009 at UMD. I will know my admission decision by April 1st.
I know a few people who applied for Spring semester after only spending fall at UMBC and got in. However, I personally don't recommend that. Transition wise, it would be easier to go for Fall. Of course, if you feel differently and want to apply for Spring, that's fine. The reason why I applied for Fall and not Spring was because UMBC posts their grades fairly late compared to other universities and I could not send in my transcript for fall yet. Also, I am a residential student and woud have to pay a pretty hefty housing termination fee since I'm backing out on my contract midway into the semester. I am not sure if they would waive this if you got into College Park and talked to them, as far as I know, you have to pay a free. They can send transcripts upon grade completition but this is cutting it close to the day of Spring Move-In. An individual that I know was put on hold for Spring admission decision because they did not know her grades yet until a few days before classes started.
My best advice is this: do as great as you can freshman year (or first semester, depends on when you are planning to transfer). Study, don't slack off and have at least a 3.0 GPA. Join a club or group that interests you or even better, do some volunteer service. Show them that they you are a well-balanced student that can handle college level courses and that will succeed at their school. Apply early as possible (before the March 1st deadline) and call the admissions office with any type of questions that you have. Most importantly, take core classes that most complete freshman year. IE, Math, English, and the Science w/lab and Science w/non-lab. Also be aware that if you intend on pursuing a degree in a field that is noted as a LEP (Limited Enrollment Program) at UMD (IE: Psychology, Government and Politics, Biology), that you should have a backup major to be in, just in case you do not get into it. If you do intend on pursuing some of those fields then fufill the basic requirements at your college that UMD students have to complete to stay in the major.
Right now, just concentrate on which college you are planning on attending next year, your plan, and finishing off your senior year well. Remember, UMD also wants to see a high school transcript that will include your final grades from high school if you have not completed at least 30 credits at your college at the time which you apply (which you will most likely not unless you apply for junior year admission).
Hope this helped!