What is the secret to great bean soup? Philly Naval shipyard had the best bean soup sold by the cup in all of?!
The secret is using a great meaty ham bone to make the stock.
Use dry navy beans in stock, cook until tender. Use a potatoe masher and mash about 1/2 beans in the stock, add sliced carrots,celery,onions (potatoes if you like) and about 1/4 tsp of Thyme. Salt & pepper to taste.
There are lots of "bean soups" so that's hard to answer without more specifics.
One thing that makes any soup or stew better though is bay leaves... and sometimes something like a little soy sauce. Of course, great stock is often important too...some restaurants let their stock simmer for 24 hrs for maximum flavor, and using bones and connective tissue is important for a rich tasting stock.