I've asked around, and I got a couple more tips. The best one, I think is this: knit a swatch. Measure the gauge. Wash and dry it. Measure again. Knit garment to post-washed gauge.
Another tip which sounds bizarre, but they swear it works: when the ribbed edges of the cotton garment have stretched, wack the edges against a counter to bring it back into shape. They say it saves on having to over-wash the garment.
KnittingHelp Queen Bee
It is not because things are so difficult that we do not dare; it is because we do not dare that they are difficult.