First, use a box. Not for fun but b/c you don't want to spill shit all over your place and have to vacuum afterwards. A box might look like this..
I base most of guys with Elmer's glue and fine black ballast from Woodland Scenics (free plug sponsor me) and I skip around leaving some areas blank so I can fit grass tufts inbetween. I like my static grass to be in clumps b/c I think it looks cool like that.
Put a generous glob of glue in each spot you want the grass and put your miniature over the container. (the dont-be-an-ass to your roommates part) Then put pinches of static grass all over the spots (generously) and push it down a bit. Turn the mini over, hold it above the container, and flick the bottom of it to remove all the unglued grass and make the stuff that did stick stand up. If there's still glue showing just do it again.
It'll look like this.
Then just drybrush a bit of glue here and there and do the same thing you did with the static grass again, this time using whatever leaves you've purchased. These ones here are from Galeforce Nine and they're awesome and you should buy them and they should sponsor me.
This post was a request, and wasn't meant for everyone. If you were thinking, "I know how to do it and idc Zealot" then it's not for you!