I always tell beginners to take it easy on their first day of weight training. That doesn’t mean you shouldn’t push yourself, but you certainly don’t want to pull a hammy trying to impress your buddies if you’ve never lifted weights before. Before you choose how much weight to lift, you need to think about the number of reps you’ll be doing. You don’t want it to be too easy—this isn’t Saturday night at the bowling alley—you want to struggle by the last rep.  If you’re going for 12 reps instead of 6, reduce your weights. If you feel pain during your reps, slow down and reduce the weight.