What string tension should you string your tennis racket?

53 lbs.

If you take nothing else from this article, I would recommend stringing your racket at 53 lbs.

It is probably the average tension selected for tennis racket tension in today's game. 

With most rackets and most strings, 53 lbs should work well.

For a more detailed answer, lets look at a few factors.

If you are using a co-poly tennis string, like rpm blast or luxilon alu power, you can string a bit lower. 48-50 lbs could work well.

Polyester based strings are more durable and control oriented, so stringing at a lower tension can help soften the string bed with co-poly strings.

If you are using a synthetic gut, multifilament, or natural gut tennis string, I would recommend stringing a bit tighter. Maybe 56-59 lbs.

These strings are much softer and more elastic, so stringing at a higher tension can help firm up the string bed a bit.

All else equal, higher tension means more control and lower tension means more power. This is an oversimplification, but lower tension will help marginally increase the launch angle.

Another factor to consider would be the racket's head size.

An oversize head racket, like one that is 103-115 square inches, will have a lot more surface area to string.

This could be an argument to string a bit tighter to prevent too much string movement.

And vice versa for smaller head size rackets, like those that are 95 square inches.

Finally, heavier rackets will play inherently more powerful. If you are using a heavier racket, like one that is above 305 grams unstrung, you could use a string set up that may help give less power or take some away if you are missing long.

The most important thing when it comes to string tension is that you are using a setup that works best for your game.

There are top ranked professionals who string in the 30's lbs, and some that even string at 70 lbs.

There is no right or wrong answer.  

It will simply be what works best for your game.

And again, if you take nothing else from this article, and still not sure: string your tennis racket at 53 lbs.