Take it Slow
If you want to jazz up your weight-training workouts and exercise your powers of concentration at the same time -- have we got a technique for you! On occasion, perform some of your exercises in extreme slow-motion. Take 15 seconds for your first repetition: 10 seconds on the lift and 5 seconds for the lower. Not only are these prolonged reps more physically demanding; but you need to concentrate and focus carefully on what you are doing. You'll need to do only 4 or 5 reps in each set rather than the usual 8 to 12. Keep a stop watch nearby to time yourself.
In the best-case scenario, you'd have a partner timing you so that you can concentrate fully on your movement, and not the time as well.
Final thought: slow-motion lifting is best suited for individuals with a good amount of experience. If you're relatively new to strength training with weights, it's probably best to focus on learning proper form before trying more advanced techniques.