To improve your running techniques you would better start slowly and then increase your rhythm lingeringly...
Warming up is extremely necessary. Believe me you don't want to start a run with cold muscles. It may lead to tweaking a bone or a joint and in the end you end up dissatisfied because you may stop before you've actually planned. Maybe discouraged too.
So here's two ways to warm up before running.
Loosen up :
Start with some light exercises to warm up. You may like aerobic exercises or maybe just walking briskly... Just keep it slow. Remember it's just a warm-up, the real show has yet to begin.
Dynamic stretching :
Stretch your muscles but keep it classically dynamic. It involves continuous movements such as kicking your legs forward, making arm circles and doing some walking lunges just don't hold on you muscles in any position.
Just start slow, and leave as much energy for the run. Keep yourself motivated and warm-up.
PS: don't forget to cool down.