said by slaterK:said by Doctor Olds:They get soaked in Simple Green (full strength from a spray bottle) then are washed and that cleans all the grease/dirt out so they look/smell brand new. Lay flat to dry.
Thats a good way. Ultimately, if you use them for long enough and get heavy grease and tranny fluid on them, they get so saturated that it becomes hard to get it all out.
Best to have a set of gloves for messy jobs and a set for not as messy jobs
Brake Cleaner will clean the grimiest one's after testing for colorfastness. 
Or the Original Go-Jo Hand Cleaner kneaded into the gloves, warm water rinse, air dry, then repeat.