How can I improve the water pressure in my shower?
This is an effective trick a plumbing contractor once told me.

Go to your local home improvement store and buy a cheap shower head (the one I picked up cost $1.50). If you look down inside of the showerhead you'll see a washer which constricts the water flow. If you take a drill and enlarge the hole, thereby increasing flow, the water pressure will increase. I didn't think it would work but it did!!

If you want to go the expensive route, there are pumps you can purchase that will attach to the piping and add pressure to the water. I've heard of such a thing but never looked for one.