I am sure that everyone here knows but just in case.....
I was helping a friend install a new switch in his cordless drill and when we started putting it back together I was ask why was I turning the screws backwards first.
If you are putting screws back into plastic if you apply a small a mount of down pressure as you turn the screw backward you will feel it pop, at that point you start turning the screw in.
By doing this you do not mess up the threads in the plastic because you are in the same thread channel that the screw was in to start.