80 grams per quart works well. Usually a day before I'll boil a qt of water and 80g of dme in a pot. Then I get a qt mason jar, put water in it and heat it in the microwave for a minute to heat the glass. Then pour out the water, dump the starter wort in the jar, screw on the top and throw it in the fridge.
It takes a couple hours to cool but now its vacuum sealed. Then I put it on the counter and pop it open when I'm ready to add the yeast later that evening.
So if I'm making a 1.050ish beer Saturday, I'll make the starter early evening Friday, pull it from the fridge around 10-11pm, and put it in my jug/flask along with the yeast. By the time I'm done brewing Saturday it's rocking and ready to go.