I had a washboard problem with my drive due to the neighbor (who also lives on the drive and owns a tractor) just trying to scrap it smooth without really understanding what he's doing.
(1) Like Sysop says, every time your wheels go over a bump, it raises your 3pt and the blade, causing another 'wave". So the solution to that is to not drive over bumps. And to do that, you need to blade it smooth and then drive over it. Which means flipping the back blade around and grading in reverse.
(2) Even doing #1 can be a pain since the blade may alternately bounce and dig into the existing 'waves', especially if the washboards are perpendicular to the drive. So I angled my blade nearly 45 degrees to slice through them. That pretty much stopped all bouncing and waving.
(3) As you may assume, I don't have ripper teeth. So this took a lot of multiple passes to dig up enough material to totally remove the potholes, which left me a very high row of driveway mix running down the drive. If you don't dig out the pot holes, just filling them in won't help as the change in material density will cause you to bounce the material out as you drive over it. The potholes just come back that way. You need to have a homogenous material mix put down as a surface and packed to the base. NOTE: If you're adding material because you want to bring up the drive, or have lost a bunch to erosion, you'll probably want to work it into the existing row of dug up material so you again get the homogenous mix.
(4) You want to move that row of material so it's in the center, more or less. You can reduce the angle of the back blade somewhat, but you still don't want it straight across. You're also going to need to put a slight tilt to it because while you spread that row out, you're going to want a slightly raised berm down the center-line of the drive so the water flows off of it. Alternatively, you can have one side of the drive raised so the water goes all to a single side, but that might feel a bit weird driving on it with the cars and trucks all the time.
(5) I forget what the recommended broken rock to sand to clay ratios are here in New Hampshire, but in my opinion, you're going to want the maximum amount of rock and just enough fines to lock them together. Too many fines and then the rock just floats around in it like raisins in ice cream; and you'll end up with a quicksand-like mess come mud season.