Different kinds of slides are used a lot in Indian classical music by instruments such as the violin and sarod but for me it is more interesting to look at some of the more recently introduced instruments like mandolin and guitar since they also have frets. U. Srinivas (mandolin) and Prasanna (electric guitar) are two good examples of how I would like to use this technique. Because of the frets the sliding has to be done in a certain speed otherwise it will just sound sloppy compared to a fretless instrument where you have more possibilities in terms of sliding slow. What kind of string you use makes a big difference and the string that fits my style of playing the best is GHS Pressurewound. A normal roundwound string will generate a lot of noise when the left hand is moving and flatwound strings, although smooth, just doesn’t feel right for me and I don’t like the way they sound in other areas of playing. The pressurewound is in between, a bit smoother and less noisy then the roundwound but still has a brightness and edge.
When it comes to the actual sliding technique there isn’t that much to it except sliding as long as your fingers have calluses otherwise it might burn a little. Speed is important to make it sound fluent and I try to put as little pressure as possible on the string. I practice slides using all my fingers in the left hand so I’m not limited to a position. I prefer using the ring finger but I’ve seen a lot of people (like Prasanna) using mainly the index finger. Since the space between frets are so big on a bass I find that using my index finger makes my hand move more which is something I like to avoid because it requires more energy and can also put the left hand out of position.