The orthodox belief is 3 to 5 sets and based on my past education in the field through the ACSM syllabus(do bear in mind that sport science like other science is fluid and constantly changes), the number of repetitions is dependent on if you want to focus and improve on:

- Muscle endurance(15-20 reps)
- Muscle strength(3-6 reps)
- Muscle hypertrophy(8-12 reps)

All the repetitions are based on your 1 rep max capabilities(google 1 rep max) and of course theories are endless and there are also endless debates about it so perhaps the more practical method is to use perceived exertion rate to gauge it but it is always good to test your 1 rep max, I do a 10 rep test but I have gotten lazier, so theory is not always feasible in the real world.

Rest in between periods is arguably more important, for hypertrophy especially, I follow the 45 seconds to 1 minute stringently, most of us will need time to build up the neuromuscular strength and fortitude to get through all 3-5 sets of this, it is extremely taxing to the mind as you get to the end of the exercise.

Of everything, I am more of the mindset that the focus on the eccentric motion with proper tempo as of most important among everything when it comes to hypertrophy and of one’s posture health.

12 reps per set does not mean max 12 reps per set but based on 50-75% of your 1RM which requires you to test but that’s tedious.

I try to optimise based on 8 reps and not go below 6 at the final sets of my workouts.

Also neuromuscular strength comes first, track your progress weekly, if it gets too tedious and hard, lower the weights.

Many bodybuilders I know lift crazy heavy weights in the gym but there are many too who do not do that but focuses on the correct tempo and range of motion and have got superior physique.