Since practice ranges are level and hitting extra balls during play is generally frowned on, it is problematic how we acquire the experience to cope with sloping lies.
Helpfully, most courses nowadays have a short-game practice area and it's here that we can develop this skill.
Chip from each of the four slopes, blending or augmenting the adjustments appropriate to both chipping and the slope.
Then on the course, look for any slope before you hit. It's often only after the ball is flying into the trees that we recognize that there was a sloping lie!