The only basis for a good soup is homemade stock. You can normally buy bones cheaply from the butcher — chicken or beef. Alternatively, you can use the carcase of a roast turkey or chicken or the bones from a roast.
Cover the bones with water, add onion, celery and carrot. Season the broth with salt and pepper. Bring to a boil and let the stock simmer until any meat falls off the bone and the vegetables are well over-cooked. Strain, reserving the bits of meat if you want to add them to your soup later.
I tend to make a lot of stock at one time and freeze it down in portions so that I always have a good, healthy and nutritious base for making soups and sauces.