Choosing the work you want to salvage can be tricky business. A few tips that might help are to pick a piece that, despite the bad parts, has some strong passages upon which to build. Secondly, only wait until you're in the mood to tackle the piece. Rushing into a salvage job can make things even worse. And finally, don't try to completely redo the picture. Pick a few key problem areas, solve those and stop. If not, you risk losing the appeal of the original work.