Soup is about just throwing in whatever you have. Generally, if there’s some kind of a meat/bones, gelatin will give the broth body. If it’s more of a bean or potato situation, you may need to pull a portion out, mash it up, and add it back in to give body. You could also temper some eggs and add them in.

If you dont have gelatin or something starchy, you can add a cornstarch slurry to thicken it. If you have a really thin broth, it won’t taste right even if it would otherwise be really tasty. Taste is an amalgamation of senses, and texture is part of that.

Acidity definitely helps soups. Brothy beans are great with a little vinegar, some soups are good with lemon, etc.