Clean Moldings Before Applying Painter's Tape
Even the stickiest masking tape won't stay put if you apply it to a dusty, dirty surface. You'll save yourself a lot of time and frustration if you start every masking job by cleaning the moldings or the wall to which you're applying the tape. Usually a thorough dusting with a damp rag is all that's required. But if the surface is greasy, you'll have to wash it with a detergent solution. TSP-PF (phosphate free), available at home centers and paint stores, is the go-to detergent for most painters. Wait for the surface to dry completely before masking.
Speed Up Painting Prep with a Painter's Tape Applicator
If you really want to speed up and simplify your masking job, buy a tape applicator. Shown is the ScotchBlue Painter's Tape Applicator from 3M. It's available at home centers and paint stores with a roll of tape, and it's designed to help you mask precisely using the adjacent surface as a guide. You simply roll it along the molding, wall or ceiling to apply the tape. Then use the built-in cutter to slice the tape at the end of the run. With this tool, even a novice can get great results with only a few minutes of practice.