First, decide what kind of watch you want.

Second, choose the band. Do you want a metal band?

Third, determine your price range.

Be sure that the watch can actually tell time. In other words, get one that has quartz, Swiss, Japanese, or analog movement. The first three use a battery while the latter one uses a wound spring. Some newer analog models have kinetic or automatic movements and store energy when the watch is worn. The movement of your wrist "winds" the watch. Be aware though that these watches should be worn daily to ensure that the "battery' is charged.

Styling may be very important. For example if you want a sophisticated, sleek look you might want to find a sleek, thin, long silver watch. For more of the punk/rock star look, you could get one with a very wide webbing or leather band. For the classy, preppy look, a metal analog watch would be nice.

Get a watch that is durable. You can't really tell by looking at one, but you can check its ratings by the manufacturer. Check the manufacturer to make sure they have a reputation of good watches.

Check for water resistance. Unless you see a marking for meters (ex. 30 meters, 100 meter, etc...) assume that it cannot be worn in water.

If you are worried about battery life, go for digital watches, tungsten watch claim for 10 years of battery life. You can also choose an automatic, this is a totally mechanic watch that winds itself.