Hi Simon
Nicks right, it's just practice.
The hardest part is learning what position to start in. Drop the handle so that it rests just a couple of inches below waist height and then lift it before you start the machine (when you drop the handle the machine becomes off balance - you have to start the machine with the pad / brush entirely flat on the floor)
Once you have this position right then its a case of lifting the machine slightly to go one way and dropping it to go the other, remembering that you always need to get it back to the flat position to keep it still. Once you get the knack it's easy. We've all been there although you're at a disadvantage not having someone with you to show you!
The cleaner your floorpad the easier it will be to control it.
Regards
Mike