Great stuff foam is expensive and despite always looking for things to foam after I finish using it for its initial task, I always ended up wasting almost entire cans of the stuff most of the time because the plastic straw becomes useless once used. Rather than buy their expensive gun and solvent, I use 14-2 romex sheath to replace the straws once used. Once done using the foam, just leave the romex sheath on the can. The next time you need it, just bend, twist, and pull the sheath off and replace. I've had luck doing this up to about 2 months after first using the can.
Great stuff foam is also useful for patching smaller holes in drywall. 2" is about the max size hole for this. Just foam in the hole, building it up around the edges and onto itself until the hole is filled. Once dried, cut it flush to the wall and brush off any fuzzies and you're ready for a skim coat of drywall mud.
If you're trying to nail into a corner or some other awkward place where you either can't or don't want to use your fingers to hold the nail while hammering, Push the nail through some thin cardboard and use that to hold the nail. It'll keep your fingers out of the way and when you're done, just pull the cardboard off the nail and hammer it home.
When taping off something for painting, paint over the edges of the tape after placed with the color that's underneath the tape and let dry. This seals the edges of the tape for the next color and what bleeds underneath matches the color that's there already.