In order of importance for intentionally targeting gaining muscle…
- Eat Protein - AIM for 1g of protein per pound of body weight (based off what you sensibly think a well muscled version of your height and gender should be)
- Mechanical Tension - Think weighted movements that will place you in close proximity to failure in 6-12 reps
- Metabolic Stress - This is usually done through limiting rest periods or performing CrossFit metcons. It can be done through higher rep ranges as well. Like 3 x 20 back squat with 3-5 minute rest (I personally think that is murder and I will psychologically burn out on it). I believe metcons are the most time efficient and also improve work capacity better, but there is a lot of nuance here.
- Damage to muscle - I believe you will unintentionally hit this regardless of which route you choose. But lowering the weight slower over 5-10 seconds will increase the potential for damage, and might also improve someone’s mobility over time.
Lastly, SLEEP. None of this really matters if your hormones are jacked up and sleeping more/better will give you better hormones than just about anything else will!