How many sets and reps should you do?
Strength, muscle size, endurance: the number of reps changes what you're training. Simple guidelines to make sense of it.

Do a little more than last time, consistently. How to apply it safely, in the gym and on the road.
Your body adapts to what you ask of it. If you always do the same workout with the same weight, it eventually has no reason to improve. Progressive overload means gradually raising the challenge so you keep moving forward.
Change one variable at a time, and not every session. Adding weight, reps and sets all at once is the fastest way to stall, or get hurt.
A good sign: you finish every planned rep with good form and still have something left. That's when to nudge things up. If the session was genuinely hard, repeat it as is.
That's what Volta's coach does. After three workouts in a sport that felt easy, it suggests moving up a level. For lifting, it also suggests a slightly heavier weight than last time, without ever filling it in for you.
Strength, muscle size, endurance: the number of reps changes what you're training. Simple guidelines to make sense of it.
Your whole body every session, or one muscle group a day? The right call mostly depends on how many sessions you can fit in.
Lifting and running in the same week, without giving up either. What it means and how to get started.