Keep in mind the distance between your handles controls the speed of the slide, the brake line in front during the direction of travel controls the altitude of the kite. The trailing brake line controls the attitude or angle of the kite .
If you want the kite low and parallel to the ground:
front brake = how high (minor control correction)
back brake = how flat (Lots of little control corrections.)
Distance between handles = how fast (Watch the sail and if it starts to flutter slow down)
Keep in mind these controls swap when changing directions.
All that being said, once you get the feel for the maneuver, it will mostly happen without a lot of thought. Don't try too hard, incremental improvements are typically permanent improvements.