In most college curricula, you'll need two semesters of science and the corresponding lab courses to satisfy the science requirement. Unless you decide to pursue a science major, that means you'll need to pick an introductory course from the choices your school offers. So how does one go about doing this?
The easiest way to choose is having an interest in one of the choices. For example, I took Biology, Chemistry, and Physics in high school and got decent grades. When I got into college, I picked Physics because it seemed most interesting. College work is much more rigorous than high school, though, and I barely passed both semesters.
If you have no real interest one way or another and you aren't planning to be a scientist, the next best approach is to examine your strengths and weaknesses in other areas. Are you a math genius? Biology, Astronomy, and Geology don't require much math; Physics can be pretty math-intensive, with Chemistry somewhere in the middle. Like animals or gardening? Biology is filled with living things, but you may want to ask if you're squeamish about dissections.
(My friend was going to take Biology until she found out they were dissecting a cat. She switched to Geology, where dissections are done with a hammer.)
Whatever you pick, it's best to stick with a single subject for both semesters. It's kind of like a freezing cold pool — once you're in up to your waist, you might as well dunk your head.
Hopefully this helps you make your course selection a bit more scientifically.
Better living through chemistry,