Which posture should I be if I wanna run faster ?

Question

I'm tall and very thin .

Answer 1

the posture that works best for you

Answer 2

Posture helps runners more than most people think.  You should always be straight up with your shoulders back.  Your elbows should be at 90degree angles, and when you pump your arms you shouldn't cross infront of your body, keep them moving straight forward and straight back.

Lengthen your stride and use your height as your advantage.  When sprinting stay on the balls of your feet.

This should help...