When stretching, as with strength training, it is important to work each of the major muscle groups. Again, that being the shoulders, chest, arms, midsection, back and legs.
I recommend you hold each stretch for 15 to 30 seconds. Is it bad to hold it longer? No, not at all, but some people find that holding it too long is boring. If it feels good and you really enjoy stretching, go ahead and hold each stretch a little longer. On the other hand, holding a stretch for only several seconds may not be adequate. I would rather err on the side of holding too long rather than too briefly.
While performing the stretch, make sure you feel it in the area you are targeting. It's very easy to go through the motions of stretching and not concentrate on what you are doing. It shouldn't be painful, but a good stretch may be slightly uncomfortable. In time, your flexibility will increase and you will need to reach a little further on your stretches.
A good stretching program may only take several minutes. Don't neglect this component of exercise because it seems insignificant. As we age our bodies tend to lose flexibility and become less mobile. Harvey Lauer, president of American Sports Data, Inc. says, "For many people, especially those over the age of 55, stretching is an important exercise in its own right." Making sure flexibility is a part of your program will be very beneficial as you get older.