Take makeup classes. There are many classes available for those who want to learn how to do makeup on other' faces. Universities and community colleges may offer students makeup classes. Some beauty supply or makeup stores offer basic makeup classes to the community every once in awhile. If you are serious about makeup you can enroll into a makeup school where courses can last up to months. Beauty schools also train students in makeup application, but you will likely have to learn another skill such as haircutting along with makeup.
Read makeup books. There are many how-to books that offer makeup application tips. They can usually be found at your local bookstore or online. You can also read how-to makeup articles online. There is a lot of information available on the Internet to help you become better at applying makeup. Video tutorials are also available online. They not only explain a process, but show you exactly how it is done.
Shadow a local makeup artist. Contact makeup artists in your area and ask if you can observe them one day while they work. You will be able to see their technique first hand and will probably also be able to ask them questions about their profession.
Practice. As the popular saying goes, "practice makes perfect." Ask your friends and family if you can practice on them as often as you can. Try out new techniques that you have learned about. Ask them how your performance was and what you could do better.