Choose a type of string. There are lots of places you can buy string online. This site I most commonly use is: http://www.tennis-warehouse.com/stringcontent.html. There are two main types of string: natural gut and synthetic. Natural gut is livelier, more elastic, and maintains tension better, but it is also very expensive and sensitive to weather. It costs about $45 for one racket’s worth of string. Synthetic string, on the other hand, consists of a wide variety of string, such as multifilament, monofilament, and polyester. Synthetic string is cheaper and generally more durable, and you can’t really go wrong with a synthetic string. You might want to look out for polyester string, however; while polyester string can provide more pop and power, it is also stiffer and less flexible, and can cause pain in the elbow, shoulder, and back. One more thing to note is the gauge of the string: the higher the gauge, the thinner the string, the lower the gauge, the thicker the string. Thinner strings usually provide more spin and feel, but are also less durable. View discussion here: http://www.youtube.com/
Choose a string tension. There’s a pretty simple rule to stringing tension: higher tension = less power but more control; lower the tension = more power but less control. Generally, players string their rackets no lower than 45 lbs and no higher than 65 or 68 lbs. I personally string my racket at 48 lbs, which is pretty loose. If you’re not sure what to string your racket at, you can’t really go wrong with any tension between 54 and 58 lbs. View discussion here: http://www.youtube.com/watch?feature=player_detailpage&v=hao7u1F6q0Y
Choose a stringer. There are two main types of stringers: electric and non-electric (pull). The difference is that with an electric stringer, instead of pulling a lever to set the tension, you simply press a button and it tightens the string for you. I have a non-electric (pull) stringer, because I don’t really see the point in an electric stringer. They are always more expensive and I don’t even really think they save much time or energy. View discussion here: http://www.youtube.com/watch?feature=player_detailpage&v=myXJm9Fxino
Find the stringing pattern appropriate for your racket. Different rackets have different stringing patterns, especially if they aren’t the same brand. This site will give you the stringing pattern for any racket: http://www.klipperusa.com/stringing/manufacturers.php. This will tell you which holes to skip, how much string you need for your racket, where to tie the knots, etc.
Become proficient . . .Practice, practice, practice.