i got a long board from my friend and i layed down a base coat of primer followed by a guide coat of a different color (i'm assuming ive done good so far?) now im not sure what grit to use to get the job done. i've heard anything from wet 400, to dry 180. so what grit do i really use to get the job done and do i wet or dry sand? thanks
-Jay

180 or 220 dry to start with.

Happy sanding!

What to do and what to use depends on how much work (staightening) the panel needs. If it's a pretty straight piece to begin with, 220 is fine. Don't apply too much pressure.
Let the panel conform to the flatness of the board.
Use a cross-hatch pattern @ 45 degrees until the guide coat has dissapeared. Of course you'll be eyeing low spots. If you find a 'deep' one, you'll have to apply more primer/filler to that spot. Don't sand it much, just enough to etch it for the next coat.
After the 220 dry sand, apply another two coats of primer/filler and block or stick sand with 400 and plenty of water.