1. Wash most or all of your laundry in cold water.
Most laundry gets just as clean in cold water. It's a simple step to take. Exceptions are washing cloth diapers, clothes or sheets with bodily fluids on them, or anything that has sopped up massive quantities of milk (such as my milk-straining or cheese-making cloths. Or spit up rags.) Washing underwear and socks in hot water is the norm, but honestly I haven't found a difference in cleanliness if I only wash them in hot every other time.
2. Use less soap.
Most people use too much soap. The recommended amount of soap on the jug of detergent is usually too much. You can be just as effective by using 1/2 the recommended amount, or 2/3 if you want to be safe.
3. Make your own laundry detergent!
If you are concerned about the chemicals in commercial laundry soap, or have sensitive skin, then make your own! There are many recipes on the internet, and I will post one here. The powdered form usually does the best, but some washers will only take liquid detergent.
2 Cups Soap, finely grated (Fels Naptha is the most commonly used kind, but I make my own organic soap!)
1 Cup Washing Soda (Not Baking Soda- washing soda. I found it in my grocery store but you might have to go to a department store or Fleet Farm.)
1 Cup Borax (I found this at Fleet Farm. Sometimes grocery/department stores also carry it.)
Mix well and store in an airtight container. Use 2 TBSP per load.
Easy, huh? :) All ingredients are pretty darn cheap, and making laundry soap isn't hard at all. What soap you use determines how "natural" the detergent is. Borax is pretty strong stuff, so don't let any little kids near it. But it's also a great cleaning agent for heavy duty jobs as well. Sometimes when I have a really messy clean-up (like cat pee on the carpet) I'll mix some borax and baking soda with water and wash with a rag. It does the job quite nicely!
4. Line-dry if you can.
If you live in a neighborhood that will allow you to line-dry your clothes, do it! It'll save you money and be better for the environment. Some people experience scratchy clothes when they line-dry, and if this happens, just add some vinegar to the rinse cycle before you hang them out to dry.
Also, they make "laundry trees" for winter use. You put the trees indoors and hang laundry on those. I love using these because in addition to drying the laundry, they also humidify your house! :) You can also use these in the warmer seasons if you put them in front of open windows and it's not too humid out.