Why does a random prompt beat waiting for an idea?
Because waiting for an idea is a subject in itself, and it expands to fill whatever time you gave the drawing. Twenty free minutes become nineteen minutes of choosing and one of panic. A prompt costs ten seconds and takes over the part that was stuck, which is not the drawing — it is the decision about what the drawing is.
A constraint from outside is also harder to renegotiate than one you set yourself. You can talk yourself out of drawing hands. Talking the wheel out of it is harder, and that is the same reason a household draws its chores rather than agreeing them.
What makes a prompt useful rather than merely random?
A useful prompt names something you can look at. “A dragon” is a genre, and it hands the blank page back to you with extra steps; “your own hand” is in front of you, has light and shadow in it, and cannot go wrong in a way you will fail to notice. Specific beats interesting, and observable beats imagined, as long as the problem is starting.
It should also fit the time you have. Put prompts on the rim that finish in one sitting — one object, one view, one figure — and keep the ones that take an afternoon on a separate wheel. A prompt abandoned halfway teaches you less than a small drawing you finished.
How do you build a prompt wheel around the thing you are bad at?
Weight it up. If hands and faces are the two you draw around, give them three slices each and everything else one: they arrive twice as often as chance would send them, and the rim shows that intention openly instead of hiding it in a list you wrote in a good mood.
Keep the wheel small and rewrite it every few weeks. Six prompts you actually draw are worth more than forty you scroll past, and the ones you have stopped dreading have done their job — take them off and put on the next thing you are avoiding.
What else is this wheel good for?
It is the plain picker wheel with prompts on it, so weights work here the way they work anywhere. For the version children play — draw something beginning with the letter — the letter wheel is the other half.
When the blank thing is an afternoon rather than a sheet of paper, the what to do when bored wheel is the same idea one size up. A list of creatures instead of subjects makes it an animal wheel.