When adjusting and before tightening - place a toothpick or thin screwdriver in the metal collar (in the playfield). Rest the flipper (with the new rubber on the bat) on the toothpick. Let the pawl rest against it's rubber stopper and tighten - not fully - remove the toothpick and make sure the flipper does not move - then tighten. I usually tap the flipper shaft with a light hammer to create space between the flipper bat and the bushing. Then tighten fully.

Should make a "science" out of it hey  

There is actually a tool (a piece of plastic) to create a space between the flipper bat and the bushing.
Its a piece of plastic the size of a popstick about 2mm thick with like a horse shoe shape on one end
You just slide between the bat and the bushing