What is the best way to fix my showerhead?

Soak it in vinegar to get the crud out.

Then attach a shower filter so the showerhead won't clog anymore. As an added benefit, you won't get any chlorine smell for a few months.

A more permanent solution would be to use a water softener.

I have read that showerheads accumulate bacteria and stuff and should be replaced. With that said, I would take it apart and see if anything is clogging it. There could be scaling from the inside of the plumbing stuck in the showerhead. Also, clear out all the holes with a stickpin. When taking it apart, pay careful attention to how it goes back together. Lay the pieces out in the order that they go back in.

take it off, open the window and throw it out the window... just kidding, very simple. Unscrew it, and fill your sink with warm water and some CLR, you can get it anywhere int he cleaning isle, rite aid, CVS, safeway, let it soak in that for a few hours, if it doesn't work, soak it in pure CLR and scrub off residue before returning to shower. This also works on rings in the shower/tub, crap burnt tot he bottom of pots and pans, you name it!

Soak the shower head in warm white vinegar.

white vinegar

turn it upside down and shake it