A lot of us have had that moment where we need to mask off a recessed area, but it's too small to press down (burnish) the masking tape with our fingers. This is a great chance to use Sticky Tack to do the work for you.
Get some Sticky Tack. It comes in different colors, mine just happens to be yellow, but I've seen it in blue and pink as well. You can usually buy this at a hardware or craft store where they have picture hanging supplies. It comes in a variety of names as well. It's main purpose is to hang posters.
Press the Sticky Tack into the area where you want to burnish the tape. Make sure to apply firm and even pressure.
Since the Sticky Tack has a tendency to stick to itself it will come up clean from your surface. Even from the small details.
You're all done. Repeat as necessary and make sure your masking tape is properly burnished to avoid paint from leaking underneath it!