Try this up against a slope
Maintain your lateral balance with your hips.
Riding slowly, drive a quarter of a crank turn with your front foot while crouching slightly to push-up on the bars and compress the front tyre. Then thrust your hips backwards and accelerate on your lazy foot for the next quarter turn. You should lift the front wheel as you push on your lazy foot.Pedal firmly but without accelerating
1° Riding slowly, drive a quarter of a crank turn with your front foot while crouching slightly to push-up on the bars.
2° Then thrust your hips backwards and accelerate on your lazy foot for the next quarter turn to lift up the front wheel.
3° Keep your centre of gravity at the vertical of the rear hub, arms fully stretched. Pull back your shoulders as far as possible.
4° Keep your knees loose, carry on pedalling slowly and feather the rear brake if you tend to accelerate too much.
5° Ideally, you should find a point of balance where you just keep the bike rolling without accelerating.
6° Adjust your lateral balance with your hips and try to maintain the same pace.
Natural progression
Control your pace until you can stop.
It is easier to learn the wheelie going up a very mild slope, the front wheel is easier to lift and the natural uphill resistance allows for better pedal control without succumbing to an uncontrolled acceleration. This also prevents the bike from shooting beneath you. Once you get the feel for it, improve your braking control, either on a flat or down a mild slope.
Adjust your vertical balance
Tune your vertical balance by hovering over the rear hub.
Often, the front wheel tends to drop down when riders don't lean back enough. For those bikes equipped with a seat, the point of balance should feel exactly the same sitting on your bike, as if you were balancing on a dining chair, on two legs only.
Tuning your lateral balance
Once the front wheel is up, use your knees and hips to keep going straight and compensate for any sideways deviations. For example, if you fall on your left, pull your right knee on the outside,
and if necessary, swing your hips aside too. Keep your knees more or less open to achieve perfect lateral control.
Start at a low speed and try not to accelerate to maintain a constant speed.
Eventually, you will be able to ride slowly, slow down to a full stop and start again while balancing on the rear wheel. It really takes some practice but it is worth the feeling.