If you didn't use filler on it yet, sand the surrounding area with 320 or 400. Put your filler on, let dry, etc. Sand that down (preferably block it). If you're repainting the whole hood, you can sand with 600 or 800.
After the filler is sanded smooth, get a few good coats of primer on it. Block sand that down too. Make sure you feather edge it real good, wet sand if necessary.
You can hand sand/block sand the whole thing but it will take a lot longer than if you DA it. Make sure you steer clear of the edges so you don't burn through. Lightly hand sand edges with 800 or 1000, or even gray 3M scotch brite.
Are you painting the hood yourself or having someone else do it?