What is a one-sentence summary of the following article?
When your goal is to increase muscle mass and strength, training every day is counterproductive. Your muscles need a chance to repair themselves in between training sessions. Without adequate rest periods, you won't achieve the body mass you want. On the days when you aren't weight training, you can still be physically active. Do cardio workouts such as jogging, swimming, biking, or even power walking to keep yourself moving. There's no need to train for hours at a time — in fact, if you train for too long, you risk damaging your muscles, which can lead to a forced rest period. Your sessions should last from 1/2 hour to an hour. Rather than training your entire body during each session, it's a good idea to split up your muscle groups so that some parts of your body have time to rest while others are getting a workout. Create a training schedule and stick to it, so you don't accidentally overtrain a certain muscle group. Bodybuilders have found that training in short, intense sessions leads to greater mass and strength than easier, longer sessions. "Training to failure" means doing an exercise until you can't physically repeat it one more time. You'll need to find the appropriate train to failure weight for each of your muscle groups to do this effectively.  To find your train to failure weight, choose a weight you can use for six to eight reps before your muscles give out. If you can do 10 reps without breaking a sweat or feeling too fatigued, you need to add weight. If you can't even do one or two reps correctly, reduce the weight. Attempting to lift too much weight before you've gotten strong enough to lift it can damage your muscles, and it's also counterproductive. Start with your appropriate train to failure weight and give your muscles time to build strength. Soon you'll find that the weight you've been using has become easy; when that happens, increase the weight by 5 or 10 pounds until you're back to the six to eight rep sweet spot. Another essential aspect of gaining strength and muscle is using the right form. If you don't, you'll risk injuring your muscles, and you also won't be training as effectively as you could be. Consider working with a personal trainer to learn good technique and keep these pointers in mind during your training sessions:  You should be able to complete each exercise using the right technique. If you can't press your dumbbells over your head with your arms fully extended, for example, then you should probably be using less weight. Another option for difficult exercises is to begin with a reduced range of motion. Gradually increase your range of motion until you are able to complete the exercise's full range of motion. Do not increase the amount of weight you use until you are able to do this. Don't use momentum to swing your weights into place. Lift with controlled, steady movements. Lower weights back to their starting position slowly rather than letting them drop. Slowing down the eccentric (downward) portion of an exercise can help build muscle.

Summary:
Weight train two or three times a week. Make your training sessions short. Train different muscle groups on different days. Train to failure. Use the right training form.