To take care of flaws and spills when painting;

When painting around trim, keep a flat-bladed screwdriver or putty knife and a clean cloth dampened with the right solvent. Then if you get a bit of paint on the trim, fold the cloth around the tip of the tool and wipe the paint away.

To scrape paint from windows easily;
Place a 4-inch wide drywall taping knife blade against the putty or wood molding. Slide a razor blade scraper against the knife blade to make a perfect line without any damage.

Removing masking tape;
If possible, always remove masking tape a soon as the paint is dry enough that it won't smear or run. As you remove the tape, clean away any paint that has seeped under the edges. If for some reason you had to delay this, soften the masking tape by blowing it with hot air from a hair dryer.

To fix drips and runs;
If you find a flaw, a drip, a run, or even a stray brush bristle when the paint is to dry to brush it out. Don't over paint it, instead get rid of it. If the paint is hard, either sand or scrape down the area. Then repaint. If the area is still tacky, hold a piece of making tape at both ends, press the tape gently over the flaw or bristle, then pull straight off, then when the paint is hard, lightly sand the area smooth and repaint.

How to touch up paint;
Even the paint is dry to the touch, it may not be harden completely. Newly painted surfaces are fragile, be careful not to scuff it. Keep a small brush and some extra paint on hand so you can easily make repairs if need be.

Tip for recording paint used;
Its a good idea to record the brand of paint, as well as the type and color used, also if it is semi-gloss or flat. A good way to do this is to mark a piece of masking tape with the information and mount it on the back of a switch plate before you screw it back on. Then when it's time for repainting or touch ups , just remove the switch plate.