In my current routine, each day has a different upper-body theme: arms; shoulders and back; and chest. I do a few leg exercises on each lifting day.
I saw good results on just 3 days a week.
I'll consider a new routine if I plateau and still need more strength.
While gaining weight, I aim for about 20 sets of 8-12 reps to failure.
While cutting fat, I aim for about 15 sets of 4-8 reps to failure.
Listen to your body.
If it can handle more sets, do more sets. If you're sore days later, do less.
On each lifting day, pick an assortment of exercises that target the muscle group for that day, with some variation week to week.