How about masking tape.

As a painting contractor, I go into homes where people have used masking tape thinking it would give them nice clean lines but really just made things look ugly.

So how do you apply masking tape so not to leave an ugly, messy job? Well first, start with a clean surface. Once you have cleaned the area, look to see if the area is smooth. If the area is rough, believe me you will never achieve a clean line. If the area is very rough, you would do better to cut the line in free hand. If you have a clean smooth surface, what you want to do next is apply the tape as straight as possible and with the least amount of pieces connected together. Now take a dull knife or metal tool of some sort and seal only the first 1/8 inch area closest to the line you want to leave. Reseal this tape line as you paint, because tape has a tendency to become loose after a few minutes.It is always a good idea to check your work as you go along to make sure the paint is not sneaking under the tape. If you have a rough area to mask sometimes it helps to run a bead of caulk over the area and smooth it out. Be sure to let the caulking dry for at least 48 hours before applying tape. Another good idea is pull the yape off before the paint dries. Happy painting.
John Howell

I want to try painting.

The best painting comes with a little bit experience and good bit of work.Everyone thinks painting is easy, but it is just like everything else. It is easy if you are experienced enough.
Well, you have to start somewhere.I think the best place for people to start is maybe taking on the bathroom. It takes a little more time to do, but everything is easy to reach.You will need a roll of masking tape to tape off the molding and drop cloth to cover the floor good. In a place like this it is easy to clean up if you make a mess. Make sure you get a good brush, and thin your paint a little so it will spread good. You got it made. So, go ahead and have fun. Just remember that if you spill any get it up before it dries and you will be fine. One gallon of paint will go about 300 sf so you should have enough paint to find out if you have what it takes to be painter.John Howell