Deploying certain rules to oneself and writing them down can help prevent picking.
To be able to follow the rules better, they should be formulated in a positive way, promoting
actions that prevent picking, instead of denying actions of picking. Only in this way
it is possible to internalize the rules such that they become a habit. In contrast, restrictions are
usually too abstract to be remembered and adhered to reliably.

These rules may be useful:
When your fingers touch your face (unconsciously, by bad habit, for example), snap your fingers. This is effective!
When you encounter a mirror, look down. (Goal: Do not look into the mirror, but this would be a negative formulation.)
When you see yourself in a mirror, stretch out your arm. (Goal: Do not go close to a mirror.)
When you step into a bathroom, dim or turn off the light.

Sometimes it may be necessary to pop a ripe pimple. To prevent further picking,
it is advisable to force yourself to only touch the face with paper and a needle. In this way,
it becomes impossible to pick unripe pimples.

When at home, one could cover the face with oil (e. g. sunflower oil butter or ghee is not recommended,
it will stink when hydrolyzed). It then becomes physically impossible to pick. But never wash the oil away with tensids;
let the oil soak, or, if absolutely necessary, wash away with pure real soap (fatty acid salts), which does not
promote acne, but still harms the skin by destroying the acid mantle.

I still find it, however, very hard not to pick. The best way to prevent it is to achieve complete healing by
avoiding to put any chemistry on the skin and by decontaminating the laundry from SLS residues.