Here's my simple formula for building muscle (training only/not diet):
Two Days Per Week
Full Body 6-8 Exercises
70-80% RM (Repetition Max)
2 Sets to Failure
Tempo - Slow so muscle tension is always maintained (3-5sec down, 1 hold, 3-5sec up)
Rest Between Sets: As long as you want
If you're to focus on one thing, let it be intensity. Meaning go to failure in each set.
Two full-body strength training days may not seem like much, but commit to it for eight weeks, I think you'll like the results.