Here's a few tips that I've found to work very well to help you get a nice fret surface;
1. Protect the fretboard by "masking off" the fingerboard. Cheap masking tape works best because it peels of easier when you're done.

2. Color the top of the frets with a red or black marker to use as a guide to see if the frets are level.

3. use a long(very, very long) leveler to flatten the frets. I actually use 3 diamond 2"x6" 320 grit knife sharpening blocks glued end-to-end on a block of wood(cheapest place to get the diamond blocks is grizzly.com..they're about $12 each).

4. Level the frets "from the side". Most people stand at the top or the bottom of the neck and run the leveler up and down the length of the neck to file the frets level. I've found that it's more accurate(takes a bit longer, though) to stand on the side of the neck and move the long leveler back and forth(the movement is from the high E side, to the low E side).

5. If you do alot of fretwork, the $100 diamond crowning files are worth it. If not, the quarter round fret files are the second best thing.

6. once you have the frets level and recrowned, sand each fret individually across the length...one at a time with a tiny piece  of sandpaper.  Use 220, 400, 600(if you're nuts like me, keep going...800,1000, 1500). Finish by rubbing the frets down with 0000 steel wool(or if you're super pickey, use white compound and a dremmel with the mini buffer wheel after the 600 grit paper).

7. TO clean up small rough fret edges: Rub a knife sharpening stone up and down the edge to level... finish by light sanding with 220, 400, 600 to remove all the marks. Wipe the fret board edge down with a light coat of tung oil if you left any marks or discoloration.

8. If you have any sharp fret corners, go to you're local dollar store or walmart and buy a women's fingernail file. One of the best dollars  I've ever spent.