I know this is going to sound obnoxiously snobby and I wish there were some other way to put it, but I feel very sad if we've come to the day when, in order to get "traditional broth taste" in soup, we have to add a dry mix.
Personally, I don't think I've ever had a home-made vegetable soup that was so bad I'd have thrown it out.
The best "tip" I can give you is that most really good soups start with some kind of stock. You can make a vegetable stock by putting a couple of yellow onions (quartered but NOT peeled), a bunch of celery, 5 or 6 carrots and 5 or 6 tomatoes (I like fresh plum tomatoes for this or you could use canned) in a large pot; fill it with water and bring to a boil on the stove. Once boiling gently, cover it and place it in a 225 degree oven over night. The next morning, pour the contents of the pot through a sieve, straining out all the veggies. Throw these veggies away--their flavor will now be in the liquid which is your stock. You can go a step further and concentrate the stock by putting it back on the stove and boiling it until the volume reduces by half or so. You should then have something approaching a Campbell's concentrated soup stock and it should have a fairly intense flavor (if it's too intense, you can always add some water back).
This stock, obviously, is vegetarian. You could make a beef-vegetable stock by adding about 5 lbs of sawed up marrow bones that have been roasted for 2 hours or so until they are dark brown (pour off the fat) to the pot along with the veggies at the beginning of the process.
Once you have your stock, make your vegetable soup using this liquid rather than water. Add new veggies of your choice--I like corn, green beans, cauliflour, carrots, celery and potatoes and so on, and simmer them in the stock until they are done--about 1/2 hour or so. If you like a lot of tomato flavor, add some more tomato too. Near the end of the cooking, you can add pasta such as orzo if you like that in your soup. Also, toward the end of the cooking, taste and add an appropriate amount of salt (it might need quite a lot since your home-made stock is unsalted). You might even find a pinch or two of sugar pleasing (not too much!).
I have not suggested any herbs--that's a matter of personal preference. If you know what you like, use it by all means. Maybe a little basil couldn't hurt, especially if you have used more tomatoes. Parsley is nearly always good and harmless. If you want a subtle "Italian" flavor, maybe a touch of marjoram.