Smooth enough for paint?

Depends on what sort of surface you are looking for. Most of what I paint has a flat or semi-gloss finish so I don't have to worry about it as much as people who are looking for a perfectly glossy finish. I just get mine so seams and filled areas don't show and then paint it.

Something along the lines of 1000 to 1200 grit should work OK. Wet sanding also works much better than dry sanding. Once you get it real close, a plain old paper coffee filter is great for final polishing (I wish I knew who I got that from here, but it works great).

There is a product called Mr. Surfacer that a lot of guys here swear by, but I haven't used it myself.

As MusicCity said it depends a lot on the kit and the finish that you want to achieve.

Let us know a bit more info about the kit and what is going wrong.

I'm really just looking for a nice shiney finish that doesn't look like it was painted by Earl Schieb.... "I'll paint any car for 99$" Not nessasarily worthy of an Enzo but just a nice smooth finish.

Best advice I could give in that case would be to not depend on your paint for gloss. Paints are pigmented and even the finest pigment is going to give a slightly rough finish. It may be VERY slight, but it's there. Get it nice and smooth and then use a clear gloss coat to finish things up. There are also special polishes and finishers designed to give a mirror-like finish. As I mentioned before, most of the things I build aren't glossy, but there are some car guys around here who can give you the best way to go.

is it for a car body ? if it is id suggest using 1500 grit. if not anything between 400-800 will be ok.

actually this helps answer my question which was unasked...

I just got through spraying my F4U-1A awhile ago and noticed that it wasn't prefectly glossy... I know it needs a second coat but wasnt thinking it was going to be so glossy either..

I am also a flat/almost flat paint kinda guy... this is the first glossy paint job I have done in my recent memory... gonna let it sit for a coupla days and future it and see how it goes... I used the nail sticks that go down to a buckskin type grit.. and got the plane body like glass so I figure the body was ok... just nervous that it isn't as glossy as the body was before painting....

If you use a primer, give it sand with some very fine grade sand paper. If you don't, sand the plastic anyway. Before painting, give the model a wash with some soapy water (This will get rid of any oils that could affect the paint). Let it air dry. Before you paint, give the model a going over with some air from your compressor (To get rid of any dust). Then paint.

Once it's all dry, decal and all that stuff, then spray your gloss clear (or matte if you want). Like MusicCity said, you'll get a much better finish with a clear coat (There is no pigment to leave a rough finish). Microscale Micro gloss does the job for me. Polish it with something like Tamiya compound, or very fine sanding cloths (like micromesh). That should bring up a nicely glossy finish.

Hope this helps.