In addition I would add..........carefully! Especially with a fillet weld. If you don't have good penetration you'll severely weaken the weld. You probably know that, but it's always worth emphsizing.

I use HW's method for fillet welds. For welds on the side of a frame rail such as filling holes I take it down with a 36 grit 3" Roloc disc on a 90* die grinder. If I want a smoother finish I'll use a worn 50 grit disc.