There are many different answers to this question. But they all depend upon wether or not you would like to play socially(with friends) or competatively (To win)
To play socially may i suggest that you learn the basic rules of tennis these can be found on www.itftennis.com and also find a good club with a popular social set up i.e club nights where players of all standards can go, you will improve by playing but you will develop your own unorthodox technique.
To play competatively i would highly recommend finding a good well-known tennis coach with an international coaching qualification, who would be able to teach you an effective playing technique and strategy, to become a more effective competative player. look on www.usptr.com to find a list of qualified coaches worldwide.