Enough. When is "Enough"?
That's almost like Orson Welles coming out and saying, "We will sell no set before its time".
I think what you mean by "more" is usually effort and not always just more weight on the bar. Am I right?
Sometimes ... sometimes, to break the "barrier" – to go up in weight – if you feel you are doing the exercise to the best of your ability, you go to a new weight.
If you are not careful with this "new" weight, you will use too much nervous energy (in that exercise).
The problem here, is in the first set or two. If you do break the barrier, your body will accept it.
You NEVER put the weight down until you've done 12 reps.
I'm not talking about powerlifting; I'm talking REAL bodybuilding.
Don't put the weight down until you've done 12, even if it is too heavy. Never. Never Fail - to do the twelve.
How's that for a tip that works EVERY time? By doing twelve you establish the FACT you can do twelve reps on that (given) exercise.