Or, I should say ‘Fretting Hand techniques’. Lefties use the right hand for these moves, obviously.
After learning the basic rolls and a few chords, students are ready to move on to several other topics, one of which involves fretting techniques. Due to the loose nature of banjo strings (as compared to guitar and, especially, mandolin strings) we have a plentiful array of uses for slides, hammer-ons and pull-offs with banjos. The looser the strings on a stringed instrument, the easier and more prevalent these techniques are.
Here are a few tips for getting the right feel in each of these three fretting hand techniques.
Slides should be done with the thumb as an anchor on the banjo neck. Use the joint of the thumb closest to the tip of the thumb; keep this spot as a fulcrum from which the sliding finger pivots. This forces the movement to come from a flick of the wrist, not the arm or shoulder. If I were to relate the proper motion of a slide to a common everyday parallel, I would say it is like sewing with a needle (but with your fingers, not your arm).
With hammering-on, you are really trying to hit the fretboard behind the string; that string is just in the way of your strike. A good hammer-on test is to try doing it without the picking hand doing anything. Just the fretting hand motion of hammering-on should be enough to give you a good sound. An everyday parallel would be swatting a fly with a fly swatter (again, with your fingers, not your arm)
Often the last of the three techniques to learn and perhaps the hardest of the three, good pull-offs can also be tested for by getting a sound from them without the picking hand. It doesn’t really matter whether you pull up (technically this is called a push-off) or pull down (technically called a pull-off); I call them both a pull-off, as does everyone else I have ever talked to. The sound is the same. I tend to do a push-off, except on the first string (at the bottom) where it is far easier to do a pull-off (it’s easier because there is no string below the first that is in the way of doing a pull-off). An everyday parallel that gives sort of the same resulting feeling would be opening a jar.
In general, use the smallest muscles possible whenever you are doing something than requires finesse (all three of these techniques require finesse). Finger and wrist-associated muscles are better than the bigger arm and shoulder muscles. Your middle finger seems to be best for these three techniques to start with. As time goes on, you’ll want to get adept at using other fingers for these techniques as well.