• Use like half the recommend amount of laundry detergent. Unless your clothes are filthy, it's plenty, it'll save you money, and it's better for the environment.
• Add 1/4 cup white vinegar as if it were liquid fabric softener (the food grade stuff, not the house cleaning stuff). This aids the detergent and acts as a mild fabric softener. It rinces completely in the wash and doesn't leave an odor.
• Use dryer balls - 2 ot 3 balls of felted wool about the size of a tennis ball - in place of dryer sheets. They do almost as well at killing static and softening clothes without the chemical residue.

And, finally...

• Wash your clothes less often. Generally speaking, unless they're visibly dirty or smell, they don't need to be washed. This doesn't apply to socks or undergarments - those should typically be washed, or at least rinced out, with every wear.

Edit: clarification, with thanks to antimidas who pointed it out!