Analyzing the flop bet

When someone raises and you call...they usually make a CB. Sometimes it's 1/2 the pot, sometimes 2/3-3/4 the pot, and sometimes less than 1/2.

What does betting less than half the pot usually indicate? Or is it impossible to tell? Any other flop bet reads that exist out there? I know nothing is certain, but hoping for some generalities and how to deal w/ it.