I have just made a vegetable soup with ham pieces in a beef stock. It doesn't taste right, it is very bland and I don't know what else to add to give it flavour. The veges are root veges like swede, parsnip, pumpkin ect. I have seasoned with celery salt and pepper but it is still very boring.
Almost any soup begins with a sweat of strongly flavored vegetables, especially onion, and then uses a flavorful broth made by boiling the life out of meat and/or vegetables.
I would recommend mixing in a diced, sweated, onion.
The other flavor that make soup interesting is umami. Easy soup additions that will give you an umami boost are soy sauce, Worcestershire sauce, fish sauce, or just straight msg. I'll put a dash of Worcestershire sauce in any soup. Fish sauce doesn't work everywhere. Be judicious.
I suppose it goes without saying that the most important ingredient is your broth. Using a nicer broth will always improve a soup. If the broth is nice enough you don't even need to add anything to it for it to be satisfying. Most soups I make are built around a broth from leftover bones and skin.
Today we had a roast chicken. Tomorrow it'll be soup.