Wash less
Unless you're sweaty, you don't need to wash your clothes after just one wear. Wait until you have a full load, it saves energy.
Use cold(er) water and air dry
Hot water is almost never necessary for your basic tees and jackets. No reason to use the dryer either in most cases, both these methods use less electricity! Save some power, money, and make your clothes last longer.
Wash inside-out
For anything printed, it's best to turn the tees inside-out as this helps keep them intact for longer, extending the life of the tee.
Sustainable laundering products
If possible, try to use environmentally friendly products, and don't overdo it. Chlorine, synthetic perfumes, parabens, etc aren't necessary in keeping your clothes clean, soft, nor smelling good!