The SAT is usually offered about 8 times a year. It usually prudent to take it at least twice (unless you make an insanely high score your first try) because most schools will take the best scores overall and not the best done on an individual test session. This will gives you the chance to work on sections that you may have weakness with initially. Ideally, it should be taken it at the end of the sophmore year or begining of the Junior. This will give you an idea where you stand and what you need to work on.
More importantly, though, is taking the SAT really necessary? If you are applying to a first or second tier school, trying to get scholarship $$$, or want to go to an out of state school, then the answear is yes. Even then there are ways to get around the SAT.
I went to Yale. My SAT's were around 1250 ( back in the old days when the SAT went to 1600). Pretty respectable and would get me into any decent state school (UT, UCLA, etc). I wanted better. I spent time researching the programs that I interested in and what kind of requirements I needed. Then I spent something 4 months writing my essay. That got me the interview. I then prepared for another 3 months just on interviewing. That clinced the deal. The first tier schools are'nt looking for the best SAT's or GPA's. If they were going to that, then all the major universities would be filled with students from Africa, India, China, Japan, and South Korea. My brother's Yale MBA class is almost half international students already. What they want is the most interesting and most promising students, the one's who are going to make a serious change in the world. Just getting a good score is not going to get you there.
If you just want to go to a good state school, just go to a Junior college for a year, get good grades (3.25 GPA), and most any decent college will let you in. It is also a lot cheaper and time effective.
