Most colleges require two teacher and one counselor recommendation. You must review the instructions in each college application to ensure compliance with individual schools.
The general rule of thumb is that you should request a college endorsement from two academic teachers. There are of course exceptions to this rule, but in most cases if you select two teachers from the core subjects, you will satisfy most college requirements.
It is best to approach your teachers as soon as possible to allow them sufficient time to compile a letter, complete a teacher evaluation form (if applicable), and submit your materials to the college counseling administrator on time.
Once a teacher has agreed to endorse your application you should inquire if they have any requirements (i.e., resume, summary highlights, etc.) of you to draft a comprehensive letter. You should provide them with a list of your colleges and the application deadline as soon as possible.
The college application is the one facet of the college transition process where the student has total control and responsibility. A student should never guess at a question or make an assumption, but rather contact the school directly if there is confusion over a set of instructions or procedure.
Finally, begin the process early, have someone that you trust review and edit your application, and always remember to send the application in early!