You should feel as relaxed as possible whilst you run. That is the idea.. but don't slouch.. remember good posture at all times.
Here are a few tips
Ensure that you stand tall with you neck and head held high. What may help is if you where to think as as though your are are hanging by a rope and its the rope is attached to your head. What you shouldn't do is lean you head forward, also having your head and neck to far backwards can also cause problems too.
You may also want to focus on something ahead of you around forty or so feet away from you. Try not to look down as you run as this will put greater pressure and tension on your neck and back muscles which may cause damage.
Make sure every part of your body even including your face is relaxed.
Shoulders at all times should be parallel to the floor, relaxed and loosely forward is best.
Did you know that the way your arms and hands move and are when you run are equally significant as your legs for running.
Your arms are what will help you drive the power and speed needed for you to go faster.
Make sure your wrists are relaxed and with no tension.
Have your elbow at a 90 degree angle with them pointing a bit out from your body. When you run and your arms start to pump they should be swinging between your waist and chest no where else.
Having you arms to high up can have disadvantages such as reduced stride lengths and you may find you wil get tireder faster.
Make sure when you arms are pumping that they don't cross over to the other half of you body.
These are just a few of the many techniques you can use to improve your running.
I will post more soon.