One Wheel Manual will demand some patience before you will execute it cleanly but if the Manuals are your daily bread you will be fine! As obvious, we are talking about the manual executed on just one wheel.
Will try not to sound too complicated so we will get straight to the point.
First, find a nice manual spot that is low enough that you won’t struggle with basics like getting on, etc. Then warm up with some regular manuals to get comfortable. The balance will be the key here so the first thing you want to do is to tighten your back kingpin as much as you can so that the back truck is nearly stone locked. This will help you keep your balance and prevent the wheel bite.
Try to get the balance on one wheel before you actually try a trick in a way that you lean back and front onto an outside and inside back wheel to figure out which feels more natural. You can do One Wheel Manual either on the inner or an outside back wheel. In both cases, you will have to find the perfect balance to stay on one wheel and not to toe or heel drag.
Once you figure it out you just go for the trick. Get enough speed and pop on the manual pad like you will do a regular manual. Before you land into Manual, lean your body weight on your back foot and press down hard to lift the outer back wheel. If you want to do it on the other wheel, lean to the front and press down with your toes to lift the inner wheel. In both cases set your back foot just where the tail concave starts.
The last step is to keep the balance which is a bit harder than with regular Manuals and the toe or heel drag are constantly there so it can take time before you will make it clean. Keep your body weight mainly on the back foot so it let you control the direction. Otherwise, it is difficult to describe how to balance it best way as when you are in the One Foot Manual it feels almost like you need to balance it from all angles.
Landing is not much different than in a regular Manual so this is the easiest part and it will come naturally. Just keep body weight on the back foot until the very end and then just drop it like you normally do.
This should be the next check on your trick list so… have fun!