I say this time and time again....your warm-up is the most important part of your workout. Without it, YOU GOT NOTHIN'. A proper warm up decreases the incidence of injury as well as improves performance. This is the case for several reasons, some being more apparent than others.
When you first start to move, your heart rate increases. This in turn increases blood flow to muscles and oxygen and nutrient delivery to cells goes up. Your body's systems are now aware that there is an increase in demand impending :)
This being said, you always want to make your warm up specific to your workout. Remember your warm up shouldn't make you tired, it should get you ready for what's to come!
Whether you are strength training, doing yoga, or running... you must warm up. And since these activities are all so different, your warm ups will be specific for each activity. I generally spend 8-12 minutes warming up.
I always like to say that the yogi's had the right idea thousands of years ago, they begin to warm the body with Sun Salutations, before initiating any rigorous practice.
Completing a dynamic warm up is going to automatically increase your flexibility and range of motion when done properly. Focusing in on joint mobility (ankles, knees, hips and shoulders) is also a great idea :)
Now I like to take things a step further. I include a third component. Posture plays a crucial role in body alignment. Body alignment is necessary for proper activation. And last but not least proper activation allows your body to handle loads safely and efficiently!
No body's perfect at least my body ain't! So in order to make the most of my workouts I have to have a great warmup!!!!
Check out this one that I use on my Upper Body Lifting Days...