How do I fix a leaky Moen shower head?

If it is around the connection area (screws on) just remove the shower head and expose the threads, then apply plumbers tape around threads then re-attach shower head.

How do I fix a leaky Moen shower head?

Let's have more details! Is the shower head dripping when the valve's shut off? Leaking from around the threads? Please explain farther. Tom

Like Tom says more info is needed.
Is it leaking from shower arm where the shower head fits or at base where the arm goes in the wall, in both cases you will need to remove the shower head or the arm from the wall, apply 2-3 turns of Teflon tape and install the shower head or the arm, watch clip.

http://www.expertvillage.com/video/58708_clean-showerhead-teflon-tape.htm

If the shower is dripping when the valve is closed then you have problem with your cartridge, please get back to us, Thanks.

John