The options you have for learning a language via self-study will vary depending on they language you want to learn. If you're interested in French of Spanish you have lots of options. If you are going to visit Africa and need to learn Twi, the choices are a bit more restricted. But if you have a choice, look for the following features in any program you consider: first, audio tapes or CDs. Humans are programmed to learn languages by listening, so audio recordings are a must, especially if they feature native speakers. If you are using a book, make sure there are a lot of drills and exercises that will give you plenty of practice. Finally, look carefully at the vocabulary words in each lesson and decide if these are words you are going to actually use. There's little point in learning words that don't have anything to do with what you'd want to talk about.