Store bought - Better than Bouillon soup base & Knorrs both make a flavorful broth.
Favorite additives: Lemon juice, cilantro, bay leaves, rosemary, V8 juice

Homemade: I keep two bags in my freezer, one for bones and for for veggie scraps. Every time I peel a potato or an onion, scrap a carrot or chop off the leaves and ends of celery I toss these scraps into the veggie bag. And every time we make chicken I save the bones (and turkey too )
Veggies - When I have two cups worth I wrap them in a piece of cheese cloth with some bay leaves, oregano and peppercorns and simmer them in a pot of water for a least an hour, skim off any foam that accumulates on the top.. Pull out the cheese cloth and toss (no straining needed and this makes a delicious veggie broth.

With the bones I crack them in half with a cleaver and then wrap them in a cheesecloth with spices and simmer for at least an hour as well, again skimming off any foam that accumulates on the top. Taste the broth, if it doesn't taste very soup like keep simmering.

Now this next step is optional and takes a little practice but try it if you want to increase your protein. Beat two eggs really well add a little lemon and then keep beating and slowly (VERY SLOWLY) drizzle in the broth. The slower the better, this way the egg doesn't curdle/cook. It makes a very flavorful creamy broth with lots of extra protein. If you add the hot broth too quickly the egg will separate and you will have little flecks floating in your soup but it will still be OK to eat.

Wow. Everyone here is so creative with broth. I just used plain old Swanson's low sodium beef, chicken, and vegetable broths, diluted because I was told to do so. My other clear liquid I was told to do was Unjury chicken broth and Isopure clear, no carb, flavored protein drink. I had plenty of variety and taste. That only lasted a week, then I went to full liquids and got to have strained, cream soups, milk based products (like Carnation Instant Breakfast) and could have my protein shakes again. Nothing was difficult because the diet progressed weekly. Don't know if I would have found the energy, though, that first week, to be as creative as you all were!

I took the leftover turkey carcass from Thanksgiving and boiled it in hot water. I added some chopped onion and seasonings for flavor. I then strained the mixture to remove the chunks of turkey. The remaining broth was delicious!