You'd learn the quickest with the help of a person who has studied Finnish. Any native speaker is helpful when you have something to go with and want to improve your skills. If you're having a hard time finding a teacher, I recommend that you find the nearest self-study course in the library or on-line and work with that. There's an lj-community solely for the purpose of teaching Finnish, something called finish_finnish. You could start there. Although I think they're basing the lessons on a text book... but they mention the name somewhere so you can get your hands on a copy if you decide to have a go.