How heavy should you be lifting ?

Unless your specific weight training program says otherwise, your goal is to use a weight that is light enough for you to do the number of reps you are trying to do per set for that exercise, but still heavy enough so that you couldn’t do additional reps beyond that point. For example, let’s pretend that you’re trying to do 3 sets of 8 reps for an exercise. The weight you use needs to be light enough so you can actually get to about 8 reps in all 3 of your sets (without reaching failure), but still heavy enough so that you couldn’t lift that weight many more times than the 8 reps you are setting out to do. Meaning, if you couldn’t reach 8 reps or at least get to within 1 or 2 reps shy of 8 in all 3 of your sets in this example, the weight is probably too heavy. However, if you did 8 reps in all of your sets but could have kept going and probably done more than 10, then the weight in this example is probably too light. The middle ground between those two points… that’s the sweet spot you’re aiming for.