Learn to do it without looking-it will train your ears. The example below shows you the same riff played both ways-the first measure has long slides and the second short slides. Slide guitarists fret with the other three left-hand fingers in addition to using the slide, although rarely at the same time. Pulls can be done by plucking a closed note and pulling the slide and the tip of the damping finger laterally off the string. In other words, don't lift the slide and the finger straight up-pull them off to the side, catching the string with the tip of the left index finger.
Pulls are easiest from the first string, but they can be done from the others also.
Hammers and pulls are indicated by curved lines in between the two notes and are marked H or P in the tablature. Unlike the previous exercises, you should practice this by playing the bass the treble together right away, without playing the treble alone beforehand. Vibrato is an essential slide technique to master, and it is a big part of the eeriness that impressed W.C. Handy so long ago. Vibrato is most often done with long notes or chords to give them a singing, shimmering quality, but it's also used with shorter notes when the slide is being held in place. The slide should not go up over the fret bar, because the vibrato won't sound right if the pitch goes sharp-it has to range from flat to normal.