I didn't think it was foamy enough, so I used more soap. So, here's my improved recipe... (though I don't pull out my measuring spoons when I make it, I just eyeball it!)
Fill your foaming soap pump to about 1/4 inch below the "fill here" line with warm or hot water. Add about 1 tablespoon of liquid hand soap. (I've also heard using dish soap works, but haven't tried it.) Put the top back on and shake to get all of the soap dissolved in the water. Viola! Done!