The younger you're taught the language, the more you'll ultimately remember. I was taught Japanese at seven years of age and know quite a bit of it, however that is the only way I've ever been taught, from an early age starting with the basics, such as numbers and the alphabet, and working my way up.
If you're serious, then you're going to have to look into professional education, as it's the best method for someone of your age (which I'm just assuming is 20's-ish)
UYI