When I made my receptacle box cut-outs in my drywall, in a few instances I ended up with up to one inch gaps between the drywall and box. How do I fill this in? Joint compound? Little pieces of drywall? I kept the cutout pieces, just in case...

 

I have dealt with this problem, if I have been able to save the cutout pieces, by applying a thin coating of wallboard compound to the edges of the cutout ( a small wallboard nail or screw, carefully inserted into the surface of the wallboard cutout, serves as a ready handle to hold the wallboard cutout, while you are working with these small pieces ) and then carefully placing the cutout piece back in the correct position. It is often useful to hold the cutout piece, which has been reinserted, for a short while, in position allowing the wallboard compound to set up a little. You may find it useful to apply a little more compound than you really need, initially, resulting in a slight ridge at the point of contact between the main wallboard and the newly attached cutout. After the compound has fully dried, a little sanding of this ridge, at the join should bring it flush, and make it ready for priming. This may seem a little time consuming and tedious, but, Hey, if your going to take the time to do it yourself, you might as well give it your best shot

 

Pre fill the gaps with mud. Let dry. Tape over gap with paper or mesh. cover tape with mud until smooth and flat.