Best thing is try and not get dust and grass in there in the first place!
I use take off and landing tables. When working from my van I have a large plastic folding table but when lugging I have an aluminium camping table. These are invaluable especially in dusty conditions where that perfect flight and WOW shot can be ruined by a glob of dust on the lens deposited there on take off.
As for cleaning baby wipes are good, they grab the dust rather than blow it or brush it else where..
Pre-flight day checks should be carried out and then every flight things like prop nuts etc should be checked.
Other maintenance is essencial. If the copter has been built by a pro they should have written a maintenance schedule which should be followed.