If its real thick you can shave the bulk of it off with a single edge razor blade laid down flat before you start sanding . . . . . Be real careful though.
There is also a tool available from the paint store that looks like a short section of a file that'll take a big run down fast too.
Bend the razor blade in a slight "U" shape so you can shave the hump/run with the bottom of the U.
Or go to your local PPG or auto body supply place and get what Crocket is talking about. Its called a nib file. Its a sharp toothed file with ridges that are mounted on a small block of wood thats like 1"x1". You then shave down the run, then wet sand accordingly. The nib files are like $18. Thats what i paid for mine at the local PPG auto body supply store, but I'm sure you can find them for way cheaper online. The rzor blaze works well just be careful.
The problem with just trying to wet sand the run is it's hard to concentrate your paper on just that run. You end up sanding down around your run/bump and by the time your run is low/level you have sanded too much around it. That makes it MUCH easier to sand through your paint(clear or single stage). So shave it very close and then wet sand the rest.
Hope that made sense.