water
ketchup
vinegar
brown sugar
the above is the basic base, the amounts of each is adjusted to your tastes.
add spices, flavorings, etc. to suit your taste.
personally I add a touch more water than needed, so it thoroughly mix, blend, etc.
and let it simmer on low heat to the thickness/consistancy to my tastes.
easy enough to do, one thing though, you might want to make/keep notes on what you done. in case you make perfection to your taste.
oh if it doesn't come out just right, add more water then adjust ingredients, etc. unless you really messed up by actually burning it, it can easily be fixed. watch the heat.
1st one I ever made
http://allrecipes.com/Recipe/Firehouse-BBQ-Sauce/Detail.aspx read the reviews for tips.
pretty good