Are
you a novice to the habit of smiling. I will suggest a begining
exercise that may help. Not only will you feel better, but it pays well
too.

S – Stretch your cheeks as far as they can go to the left and the right.

M – Make yourself hold that position.

I – Inhale, but hold your facial position.

L – Lighten up your stance by tensing and relaxing your muscles.

E – Enjoy the giggle that is now turning from a checkle to a cackle.

Practice this process until it comes naturally. Maintaining the habit
will not be nearly as challenging as starting. Others will reinforce it
by miling back and you will feel like a million dolars.