On the side of my house I have brought in lots (1-3' deep, 15' wide) of dirt (very rocky and not so rocky) i plan putting gravel down on top of it for a drive way/RV parking. What prep work do i need to do before I lay the gravel down on it ?
1-3 feet deep? Just dumped? Spread it out and wait for spring, unless you want to move most of it off to the side and put it in right.
If you need to build a driveway up by that much, you need to spread 4-6", compact it, and spread 4-6" and compact it, or, having not done that, you need to let the freeze/thaw cycles of Winter take care of that for you. If you don't have winter freezes, then time and driving over it may eventually get there, but it will still sink at random if not well-compacted when placed.
If you attempt to compact it while it's 1-3 feet deep, it will appear to have some effect, perhaps you'll move stuff around to make it seem level, and by spring you'll have an extremely bumpy mess as the base settles over winter. You can only effectively compact a thin crust (4-6") over a pile that deep. The base will be unsettled under that crust.
If you spread gravel/stone before you get the base resolved, you'll need a lot more gravel/stone in spring to fix the holes.