Tools?

I need to cut out some glass work i did and smooth it all out (i mounted the f*cking tank mounts about 2" too far forward!) When i originally ripped out the old stuff last time i seamed to have a hell of a time with the grinder, it wanted to jump all over the place and it wasnt going very smoothly. The end result was a lot of sanding.
I watch shows all the time and i see these guys allways grinding metal, glass, etc and they make it look so easy and so smooth. I think i'm just using the wrong tools.
Any of you guys recommend what kind of wheels i should use/buy for cutting glass, smoothing areas out, etc and also where to get them, i went to lowes because it was close but they dont really have that great of a selection.

try using a 7"grinder with sandpaper disks - easier to control -- after you lay ryour mat down are you flowing the resin for a smooth finish ?

Thanks,
the first time i didnt have the roller dilio so i ended up with a lot of resin, sharp edges, and a few air bubbles. I got one of those this time, hope that will solve those problems.