After lifting weights, how many days should you rest before lifting again?
Depends on intensity/recovery, programme type and goals. For example if you're doing heavy deadlift it may take 7–10 days to fully recover and if your goal is muscle size then you will want to maximise your rest over that period in order to maximise growth and possibly do some upper body work and/or some very light lower body. If you're isolating muscles then you can train more frequently but less so with compound i.e. multi joint exercises/movements like deadlift, squat, bench press. For example, upper body/lower body split e.g. arms, legs, and agonist/antagonist e.g. biceps (front of upper arm), triceps (back of upper arm). Still allowing a few days rest per body part depending on size and quality of rest e.g. quads (front of upper leg) will take longer to recover than biceps as there is more muscle mass/fibre to heal. There's a great table of training guidelines for different goals by Mel Siff, a leading sports scientist and strength and conditioning coach. Making lots of large assumptions, if you train mainly with compound lifts 3–5 times per week alternating between pushing and pulling and alternating between heavy and light sessions that should give most people good results.