Learn a foreign language by immersion
The best way that I have found to learn a foreign language is immersion. This is based on years of High School and College level classes, travel to foreign countries, as well as the use of the language immersion program Rosetta Stone.
Immersion works because it allows you to learn the foreign language the same way you learned your native language. When you were a baby, you weren't asked to learn 20 vocabulary words everyday then get pushed into learning conjugations (which is the #1 complaint I've heard from everyone who has failed at learning a foreign language).
You learned words slowly... usually the first words were the ones most important to your survival. Mommy, daddy, bottle (probably sounded more like "baba", but you knew what you meant, as did the person you were trying to communicate with). Pronounciation wasn't as important until later on.
Eventually you became fluent because you learned the language at your own pace and in the way that made the most sense to you. If you have the luxury of travel and time, immersion in the actual culture is the best way to learn a foreign language, but if that isn't an option, from my experience, the next best way is to try a language immersion program (I believe Rosetta Stone is the best, but there are other similar programs available).