Use denatured alcohol (if you can find it) (the best) or use rubbing alcohol (not as good but still works).

I will not recommend using soap and water which so many people recommend you to do because if you get some in your phone, you have to wait for a few hours for it to dry out before you can put the battery back in.

Alcohol dry out faster so if you get some in the phone, you only have to wait for few minutes.