For me, it means that at each workout and for each exercise, you reach a point of failure, you just cannot do another rep, your muscles are just plain dead.
Do you reach that point of failure?
Most people think that they do but they actually maybe are not even getting close to it. This is especially true on exercises where it's dangerous to be in such a situation like a bench press. You don't want to be stuck with a 100 KG loaded bar on your chest... and this prevents you from going to your maximum level.
This is why you either have to select exercises that allow you to reach that point of failure like pec flies, anything with dumbells, machines or have a partner for more dangerous stuff like squat or bench pressing.
How many reps?
Your weight must be high enough to hit from 8 to 12 reps on each set. If you do more than 12 then you need a higher weight and the opposite if you can't do at least 8 reps in proper form.
That's critical, an uncontrolled rep without proper form doesn't mean anything, it doesn't count and has no value, 8 to 12 quality and controlled reps!
Yes you need rythm, most of the time, 1 second contraction, 1 second pause at the peak and 2 seconds to go back to start position is right. Do not skimp on the negative 2 seconds (going back to starting position) and contract on that peak!
Keep a log of all your workout and make sure that each one is a little bit harder than the last. This is really import for grow. Say that last time, your last set was 10 reps, this time you need to reach 12, it it was already twelve then you MUST add weight. Muscles only gain when they have new stress else, they don't have to and they are even more lazy than you!
To be continued...