Re: multani mitti
Making it into a paste with rose water is really good for the skin. You can also use lemon juice to make a paste; since lemon juice works as an astringent, it should help with acne. Leave it on for 10-15 minutes. It'll get all dry on the skin.. Wet your hands a little and use that moisture to massage/scrub the paste off your skin. And then wash your face of course :)
There might be other ways to use multani mitti, so others can probably chime in too..
hope it works for ya! :)