Before making my own broth I thought it was way more complicated. Sure, there are specific broth recipes for specific soups but I throw all of that out the window. I save tiny onion ends, carrot scraps, tomato bits, asparagus clippings, and throw them in a plastic bin that is kept in the freezer (actually it's two 64 oz plastic containers). I even end up using the green ends of leeks ESPECIALLY when making potato and leek soup. Its just crazy for me to throw all that fabulous aromatic greens. When washing leeks keep in mind to wash them, then again, one more time and then you are done.
Good rule of thumb is to have one part veggies to two part water. Sometimes but not always I throwing in 2 bullion cubers (MSG free), a bay leaf or two & some peppercorns. Bring to boil & simmer for an hour. Let cool & strain. I started to use a cheese cloth to get out the tiny bits of veggies that break apart.
If you aren't using it right way, after the broth cools, pour it into ice cube trays and let freeze. Remove from tray and place in a freezer friendly ziplock bag for longer storage.