The ollie manual is a good trick to help your balance and ollie control. The idea is to ollie and land on your back wheels, riding a wheelie for a distance before setting the front wheels down. It can be done on the flat ground or over an object, but is most commonly done up onto an elemant, like a curb or a block. It requires a fair sense of balance, and you should be comfortable ollieing. It might be good to get accustomed to manualling on flat ground before ollieing onto something. Ride at the curb at a normal ollie speed- you'll want to go fast enough to get up onto the curb and still have momentum for the manual. Pop into an ollie and get over the curb. Insted of levelling the board in the air beneath you, keep your leading foot up and your weight centered over the back wheels. The lower you pop your ollie, still clearing the element of course, the smoother you will land on your back wheels and the easier it will be to gain balance once on those wheels. Once on themthere back wheels, you'll notice your body arched forward over your board as you ride the manual. This is how you kepp your weight balanced on the back wheels.
Ollie manual