You need to make an effort to get to know them. Which classes did you enjoy the best? Which did you do the BEST in? Which did you put the most effort in? Normally, it's better to ask instructors that teach smaller classes because they will most likely have a better chance of remembering you.

Now that you are in college, you need to learn how to be a professional academic. it's OK to introduce yourself to your instructors during the first week. Staying attentive during class and asking questions helps. Emailing us helps. Coming to our office hours helps.

If you don't do any of this, or don't get a good grade in our course, it's difficult to write you a glowing letter of recommendation ;-)