Make sure you don't over exert yourself or expose yourself to any sort of debilitating injuries when your body hasn't acclimated to a lifting routine. Get plenty of rest/sleep and ensure also that you are consuming as much protein as you need to achieve whatever your goals may be. The effects and general efficacy of lifting is greatly enhanced by proper diet and rest as that is the triad of making gains (lift, eat and sleep). Focus on heavier lifts with lower reps and fewer sets for muscle mass and greater reps and sets at lighter weight for a more lean and athletic look. Go and research pre-workout supplements and find the one that is best suited to your needs. Or, I can recommend a few here.