1) Go for timeless colors, don't do anything stupid like acid wash, because it just looks weird on men.
2) Go for timeless styles- you want to find the exact pair that will be timeless forever and classic styles will be timeless forever!
3) Choose the right pair for your body type: Guide here
4) Make sure you are buying pre-shrunken jeans
5) Make sure they can handle all your stuff, like wallet, keys, phone, etc.- so it never hurts to try them on in the store before you purchase