Step 1- Get good armor and a ride with darts.
Step 2- Don't be a pansy
Step 3- Go out there and shoot the Rex in the face to show it who is the man

Don't move..... They can only see movement. Stay complet- Wait, why is it walking towar- OH GOD NO HAVE MER-......

There once was a rex called Paul,
Who stood about 15 feet tall,
Use tranq arrows or darts,
Straight to his heart or
You'll struggle to tame him at all.

You don't have to be faster then the Rex just faster then your tribe mate.