Here is a quick and simple recipe that I have been using for the last year:
1:1 ratio of borax and WASHING soda
1 grated bar of natural soap, the kind you find in the organic section of the store. I personally like lavender because of it's calming effect
a couple drops of essential oil in whatever scent you like.
Personally I like the grated bar of soap more.
Just mix it all together in a big jar. I use a large glass storage jar that holds at least 12 cups, and I make about 10 cups at a time
When it's laundry time I use about 2 Tbsp in a load, sometimes less sometimes more, depending on the size of the load.
This recipe works great for me, I even wash my cloth diapers in it. Most times a recipe calls fro Fells Naptha soap or Ivory, but I have skipped out on that product and just used the organic soap...no chemicals and it smells nicer.