I have found that chicken broth or stock does not thicken as easily as beef broth or stock will. I often find myself adding too much flour or cornstarch, hoping the chicken broth will thicken, but in the end all I have is starchy tasting almost-gravy.   I guess what I'm asking is what's a good stopping point, how not to add too much cornstarch? ...and is there a way to get rid of the starchy taste if I go past that point? 
None of the answers so far mention collagen -- specifically, using a stock made from roasted and cracked poultry bones.  You don't have to roast the bones, but you do need to crack them -- use a large, heavy knife or cleaver (not a chinese vegetable cleaver, you'll screw up the edge) to chop the bones up into about 2" to 3" pieces (5 to 7cm).  Put them in cold water, and slowly bring it up to a simmer, and just leave it simmering for a few hours.  You can add vegetables, too, but you'll want to pitch them, as they'll have been overcooked by the time the simmering's done.  Then strain everything, and use that as the base of your soup.  If your refrigerate stock that has enough collagen in it, it'll set up like jello, and hold its own shape.  Starches can work, but they're not ideal for soup -- flour (unless cooked as a roux) leaves a raw flour taste and cloudy soup; tapioca leaves little granules in there; corn starch will break down if you cook it too long. 