Extra steps for a first-time usage:
a. Adjust the elastic to a comfortable length.
b. Straighten up and then sit down. You should feel a gentle tension and not much more. Both on your feet and on your upper body. It is more than enough. A more noticeable tension would be uncomfortable fast. And remember that having that perfectly sleek and straight shirt line is not ideal either. Too noticeable and it will appear unnatural and will raise few eyebrows around you.
c. If it doesn’t feel perfect yet, adjust everything again. Take your time, your first experience would feel even greater.