Don't fall into a routine where your workout is the same day after day.
Think about your workout, and plan what kind of exercises you'll be doing. Do low reps and high weight on one day to build strength; on another day, do high reps with lower weight to build endurance. Use as many kinds of weights as you can -- alternate among free weights, cables, elastic bands, exercise balls, and your own body weight. Remember, you'll get the maximum benefit when you don't go too fast, and you pause when you reach the extremes of your motion.