Enroll in a Hindi language course. Attend every session, study regularly and do your homework. If you need more help speak with your teacher, study with other students or look for extra lessons online. Use a tape recorder to record your teacher's pronunciation of Hindi letters and words so you can practice with this recording at home when you study.
If you prefer to study on your own, go to the Beginner's Hindi course website (see below) and go through one lesson each week. Make sure you understand the material completely before moving on. Go to NYU's Virtual Hindi website (see below) for multimedia learning material and follow the lessons in the order given according to your own pace. Purchase a Hindi language textbook and dictionary to supplement your online learning tools.
Post an ad on the Craigslist website or in your local newspaper to find a native Hindi speaker to tutor you or to do a language exchange with. Be sure to meet frequently to make the learning effective.