A strong and powerful tap swing is the fundamental basis of developing the power needed for a variety skills, such as long-hang pullovers, flyaways, and giants. Many gymnasts don't understand the mechanics of the tap swing, and as a result, don't understand why some of their skills are slow in getting around.
Put simply, tap swings are just swings back and forth on the bar. If you experiment for long enough, you could figure out the best timing of when to "pump" so that you get the most energy out of it. Ideally, your body should be extended and slightly arched just before you hit the bottom of the swing, and you should snap back into a hollow body position once you pass vertical.
One drill that can be done to become comfortable with this "hollow-arch-hollow" pattern is to drape a panel mat over the low bar and do tap swings on the high bar, kicking backwards enough to touch your feet on the draped mat.
Gymnasts learning taps tend to pull in at the top of their swings. In other words, rather than the shoulder angle being as open as possible, the gymnast pulls her chest slightly towards the bar. This begins to happen when they are told to swing higher and to point their toes at a higher target. Pulling in tends to slow down the swing earlier than an open shoulder angle.
If you find your tap swings are loose at the top, rather than hollow and tight, you may need to strengthen your abdominal muscles. Hollow Hold Rocks are an ideal exercise in developing the required muscles, and to get the feel of being hollow.
Once you get stronger and more powerful tap swings, you will notice many of the skills that require them are becoming more powerful themselves, and much easier. Keep working at them, and good luck!