Techniques vary from person to person. All I can really do here is give you some things to avoid and good habits to practice. First off always remember to burnish the tape down around its edges. This is especially important on very thin tape or pinstripe masking. Failure to do this will result in paint leaking under your tape an ruining your work. Use yellow 3M masking tape for pinstripes. The blue stuff is a bit to thick for super fine lines.
When masking a line that is very tight don’t use the outside/inside edge of the tape, it can be rregular and cause imperfections in the line you are trying to make. Instead cut the tape down with an X-acto knife, creating a razor sharp edge to mask with. I just tear off a piece and stick it on some clean plexi, then use my metal straight edge to shave off a few mm from one or both edges of the tape. If you have to mask some compound curves or flames, use tape that is about 1/8″ in width, if you can’t find tape this size cut some down like mentioned above. Thin tape will bend and flex into a curve easily.
A good habit is patience. When you are doing a multi-colored masking/paint job wait a day for dry time of each color. If you pull the tape off too soon the paint will not “cut” as you remove the tape (see the image below for a visual on “cutting” with tape). By pulling the tape off at a steep angle away from the paint it “cuts” the edge reducing the chances of leaving an irregualr painted line.
Mask and re-mask; on complex jobs you may have to remask the part many times as you complete layers of the design. Don’t be lazy and try to skip this, too many applications of paint on the tape will cause it to shrink and pull away just enough to allow bleeding, ruining your work. When in doubt remask the part. Try not to leave the tape on for extended periods of time, like say, a month.
The tape will break down over time and may leave its adhesive behind when you remove it. Even good tape can fail. Avoid leaving a masked part in direct sunlight, the sun can wreak havoc on some tape, causing it contract and expand as moisture evaporates from the paper. The adhesive can also melt and be forever stuck to your work. When removing the tape, if you get some small areas where the adhesive has stayed on your part, don’t try to rub it off or wash it off.
Instead use a new piece of tape rolled up and dab the sticky spot. This will almost always pull that leftover glue off. When taping a curve always cut about 3 times as much length as you will need. It is easier to work with and bends better if you have about 6-10 inches of tape to hold on to and maneuver. Avoid creases in the tape. Creases can lead to paint bleeding. Keep the tape as flat as possible. If you have to pull the tape off the work piece to many times it will stretch and you will not be able to make a straight line with it. Do the right thing and tear off a new piece to work with.
