The best way to fix it is to replace the stem or cartridge. You have to take the handle off and any other trim that is covering the stem. Turn the water off and remove the nut(if any) that holds it on, sometimes it doesn't have anything holding it down, it might just be screwed in. Remove the cartridge and run down to the store and match it up. Make sure you get the hot or cold or both, some only turn one way and won't work on the cold side or vise versa. If you leave a MSG in my shout box with what type of faucet it is and what company made it, I might be able to give you more info.