I first saw this in the Tightwad Gazette several years ago, but have since seen it on websites and blogs such as Laines Letters. Use less than the recommended amounts of products such as laundry detergent, dishwashing liquid, fabric softeners and other cleansers. Keep decreasing the amount you use until you reach the point that it matters. The manufacturers want you to use as much as possible!
My best success with this is that I use 1/2 a fabric softener sheet. The best one at the best price I have found is the Clover Brand at Dollar General. There are 50 sheets for $1.00. I cut them in half and I can't tell any difference in the softness of my clothes. They have a good smell, too. Hey..... maybe I should try 1/4!!! :).
Laine of Laines Letters recommends using 1/2 the recommended amount of laundry detergent, but let the washing machine agitate longer or let it soak overnight, depending on how dirty the clothes are. One of my sons doesn't get his clothes dirty at all, so his can wash with less detergent for less time. HOWEVER, the other son gets his clothes extremely dirty, so more detergent and agitation for him!
I also apply this principal to toothpaste. 1/2 squeeze is just as good!
These are small savings, but they add up over time when combined with other savings.