It's very easy on the ground. You ask for the sideways movement by asking certain parts of the horse to yield. As soon as they yield, then you release pressure. They may go backwards, they may go forward. But as soon as they go sideways, release pressure. To get them to turn on the forehand, you ask them to yield their hind over by asking their hips to yield. Be careful about not getting kicked. To do turn on the quarters, you make them yield their shoulder. The easiest way to do this is flex their neck so their nose is tipped inward and them ask him to yield via applying pressure until they move.
Now for a sidepass: you yield the shoulder, yield the hind. Little by little
Obviously best to work on yielding certain bodyparts before you do full out lateral yielding.
Does that make sense?
Now you ask for that yield either with an even pressure (flat hand is less noticeable than say one or two fingers) or with motion (if they are good at reading your body language)
"Strength is the ability to use a muscle without tension"