Fixing a leaky shower head is simple. First, remove the shower head. Check the screen and rubber rings to make sure they're not damaged. If you notice sediments inside the showerhead, clean it with a vinegar solution. When you're done, rinse the shower head.
You can also use sealant tape to wrap the shower pipe. Place the showerhead on the shower pipe extension and tighten it by hand or with a wrench. When you're done, turn the water on and see if it's still leaking.
If you need to fix a rainfall shower head, check all the components and make sure you've assembled it correctly.