If you are lucky enough to have a hard wire lighting fixture above your shower take advantage of it. If your current fixture isn't bright enough perhaps you could start with a higher wattage light bulb. Most fixtures have a label next to or under where the light bulb screws in, which tells you the maximum wattage this light fixture can handle safely. If your current bulb is less then this (it says in very little letters and numbers along the base of the bulb, which is the silver screw in part) then just buy a higher wattage bulb. If your light fixture still isn't bright enough for you, perhaps you need to change it out for a new one. Sometimes the type of lighting enclosure is filtering the light badly, perhaps the light fixture is old and not performing well, or maybe you need something that takes more then one bulb. Remember when buying a light fixture that goes directly above your shower it needs to be enclosed to protect the electrical parts from the water. A glass globe, a plastic dome, or a florescent light fixture with a ceiling flush plastic covering are great options. You can replace the fixture yourself by carefully following the directions, you can get a friend with some experience to help you with it, or you can hire someone to do it.
If you aren't lucky enough to have any hard wired ceiling light fixtures in your bathroom, you can still have a ceiling light without being a master electrician. This type of lamp is known as a swag lamp. These are the kind that look like a pendant light fixture, but are on a long cord which is surrounded by a long chain. All you need to install a swag lamp are two ceiling screws (they look like little hooks) and an electrical outlet. It's best to locate a ceiling beam to attach the screws into, but if this can't be done buy the type of ceiling screws that work on just drywall (sometimes known as butterfly screws). Screw one ceiling screw near the shower. You want this light fixture outside of the actual shower as a safety precaution, so place the screw near the outside of your shower curtain. If you have a shower door place it near the outside of it but clear of the door swinging out (test it to make sure the door doesn't hit it). Then you screw in the second anchor 2 to 3 feet away from the second. Hang the light from the first screw, then swag the chain over to the second screw for added support. Plug the cord into the outlet and turn it on. See, anyone can install a swag lamp. The only downside of this type of lighting feature is they are getting harder and harder to find in the stores. If you can't find one you like or can't find one at all, most home improvement stores sell swag lamp kits so you can make most any conventional light fixture into a swag lamp. This will require a little more skill but these kits are fairly self explanatory and definitely don't require expert electrician knowledge.