Wet Sanding

If you're asking this sort of question you really should not be attempting to paint the hood of your car! It's the most prominent part of the vehicle and unless you have the skill and professional equipment and access to a spray booth is most definately not a DIY job.
In answer to the question you need to "key" the whole surface to be painted. If the surface is unblemished (no stone chips etc) then you can key it with a scotchpad. Wet sanding is for between coats and to flatten off primer and/or filler if required. You never dry sand anything on a car body.