Every morning, after brushing my teeth and having my breakfast, I look forward to putting on my shirt. A daily routine, I take the shirt out of its protective laundry bag, slowly remove it from its hanger, then drape it across my shoulders.
Respect your shirt, and it will respect you back by making you look your best.
I always take the small effort whenever in the toilet to re-tuck my shirt. It feels great to have a freshly tucked shirt, and that makes you look great too. Many office workers like to have their shirts half tucked out after work hours, and I personally find that quite gross.
Lets reserve the revealing clevage for our lady friends, or even for weekend shirts. Office dress shirts are meant to be worn fully buttoned up, preferably using mother of pearl buttons that shines and glistens in the stark fluoroscent lights.
And do it well. That means crisp collars, impecceble front panels, sharp cuffs and flat yokes. A sloppily ironed shirt instantly loses any respect people will give you. For more information, see here
If you wear a necktie, you must button the dress shirt to the top. While the shirt is buttoned, you should be able to slide two fingers between your neck and collar.
For informal usage, you can leave the top button unfastened. When you bend your arm, sleeves should be long enough so that cuffs do not ride up your wrist when you move your arm.
Don't be afraid to roll your sleeves up when necessary.
In general, a shirt will last two years. Chili parties, leaky pens, sip-tops, the world is full of ways to ruin good fabrics!