Dice all the vegetables to approx the same size. The smaller 1/2 inch or so, you dice them, the shorter cooking time you'll need to extract the flavors.
Place all the vegetables into a large stock pot and cover with cold water.
Bring to a boil, and reduce heat to a simmer, cover and simmer at least 20 min.
Strain the liquid into a bowl. If you want it really clear, run it through a fine sieve a few times. Toss the veggies into the compost bin.
***I have a pasta pot, with an inner pot, that is a colander. I used this to cook my veggies in and strained them right out of the stock.
****You can use any combo of veggies, but stay away from the cabbage, kale, broccoli family...their flavors are too strong. Also, stay away from potatoes, they absorb flavors. Play around with different spices too.