Slide technique should be so simple.....right?
Just move the slide to the right place at the right moment...right?
Well knowing it and actually doing it can be two different things. Here are two exercises that may be helpful. Neither one is original.
In legato, we want to stay on each note as long as possible. So, that means move the slide at the last instant (while staying relaxed...I like the verb "flick" as in "flick the slide at the last second")
Another trick I've seen pertains more to speeding up the slide in tongued passages. It involves moving the slide right after the note sounds:
It never occurred to me that these two exercises are so yin and yang. In the first, you move the slide at the last possible second. In the second, you want the slide in the next position at the earliest possible second.