Of course, the only way to be 100% certain that you won't become pregnant is sexual abstinence. With that being said, there are many different contraception methods that have very high percentages of success, and very good results. Determining which are the best for you is best decided in conjunction with a detailed history and physical exam which can be performed by your OG/Gyn. In fact, if you are sexually active, I would recommend routine visits with your OB/Gyn anyhow.
Contraception, in general terms, is a term that refers to techniques that prevent fertilization. Contraception techniques includes barrier methods(such as condoms, and diaphragms), oral contraception (also known as oral hormonal therapy), implantable hormonal contraceptives, and injectable contraceptives. Each of these methods have their own positives and negatives, and each has its own percentages of success rates associated with them. There is no way that through this forum I can speak with any specificity. It is also crucial to remember that the only birth control
methods that also protect against sexually transmitted diseases is condoms used properly. I would definitely recommend setting up a consultation with an OB/Gyn to discuss your questions.