The key is to wet sand with progressively finer grits of sandpaper all the way up to 1200 grit wet/dry. When sanding, try to use even pressure and avoid "finger pressure points". Keep a clean supply of fresh water on the sanding area.
Afterwards, you can begin buffing with a ROTARY High-speed buffer and a WOOL pad @ about 1800 rpms using a heavy buffing compound. Keep it moving and be careful around corners and edges to prevent "burning" the gelcoat.
Then you can work your way up to a finer polishing compound, and finish with a wax and fine polishing pad still using the rotary buffer. Note: Orbital buffers don't create enough pressure to polish the surface, but they are fine for applying wax.
If you're in Va. Beach, I can help. I also sell waxes & cleaners @
www.waxingfrenzy.com
*Our wax will remove black streaks without sanding.
Hope this helps,
Capt. KW