Begin by learning the alphabet. Hindi uses an alphabet and script that are different from English. Learn to write the letters and to produce their individual sounds. You can use online video tutorials to hear the sounds and see the letters written such as those found on YouTube.
Move on to learning common phrases and words. Listen and read for words and grammar structures that you recognize as your vocabulary builds so that you can understand the gist of something that is spoken or written. Look for words that are used often in conjunction with the words you know to help you build your vocabulary.
Join an online language exchange like My Language Exchange, or meet regularly with a Hindi speaker to improve your conversational skills. You will learn new words more quickly if you hear them and can produce them on your own. Write e-mails to Hindi-speaking pen pals so that you can improve your writing. Speak, listen to and write in Hindi as much as possible to improve your language skills.