No Man's Land
A good way to tell if you're doing this properly is to video tape yourself playing. Watch the video with no volume and see if you can tell what rhythm you are playing. I find that the people with the best slide technique often have a slide motion that is clear enough that a rhythmic dictation could be taken from it. Try your best to move the slide in a smooth, deliberate fashion that reflects the rhythm you are playing. In an effort to do this, please resist the temptation to jerk the slide in a muscular, uneven fashion from place to place. The goal is to find a nice balance between clarity and fluidity. It takes a lot of practice but makes a huge impact on the precision of your playing when you get it right.