Are you getting into a fitness rut? Doing 3 sets of 12 reps of everything you do getting a little old? If so, think about incorporating a single set workout (high intensity training) into your routine every now and again.
Single set strength training (high intensity training) stresses muscle exhaustion in less time than the typical 3 sets. You probably currently lift 75% of your max resistance 10 times for three reps, but high intensity means lifting a higher percentage of your max resistance for a shorter period of time. For example, if your max (amount you could only lift once) is 10 pounds, instead of lifting 7.5 pounds 10 times for three sets, lift 8.5 pounds (85% of your max) until muscle exhaustion (until you can't do it again). It could as little as one rep, as long as one rep completely exhausts the muscle, but most people can lift 85% of their max 6 times.
Be sure not to go above 85% of your max (if your max is 100 lbs, don't go about 85 lbs) because that could lead to injury. Remember to breathe during the concentric (lifting) part. Always give the muscles you worked at least 48 hours rest before working them again. Also, it is always a good idea to use a spotter. Remember the name of the game here is quality not quantity so make sure that you're using proper form. I do not recommend doing a high intensity workout daily, but rather adding it once a week or so to spice up your workout.
Fit's Tip: Working at higher intensities also shortens the duration of your workout.