Stuffing your pockets with keys, change and other assorted items will put strain on the seams, so just don't do it.
You should unbutton your suit jacket before you sit down otherwise you will be pulling on it. Also, as you are sitting down, pull your pants up at the thigh just a little so you don’t stretch the fabric too much. Both of these things will also make you more comfortable.
A clothes brush is a great thing--brush your suit with one when you take it off to keep it clean and looking good. This is something my father used to do and I remember watching him do it, and now I know why.
Hang your suit on a good wooden hanger that is made for suits and store it in a breathable garmenrt bag for protection. And avoid cramming it in between lots of other clothes, which will cause it to wrinkle.
Dry clean your suit only when necessary but at least once a season. In between cleanings, have it pressed or steamed and spot clean when required.
