When I make my vegetable soup ( which is basically a modified Minestrone soup)
I usually use a 1:1 Tomato to Veggie broth ratio. I literally take a 28oz can of tomatoes ( whole(with tomatoes broken up a bit ) or diced, and then i just fill the can up with veggie broth.
If I want a thinner soup, Ill use a little more water. If I want a thicker soup, Ill often blend up some of the beans (1/4 to 1/2 cup) with some broth and then dump that in. ( my daughter and wife prefer it thicker, I like it a little more soupy).
As for the veggies, I usually fry up a diced onion, diced carrot and diced celery with olive oil, usually with a little salt to sweat it a bit ( I dont want it to brown). If Im using fresh string beans, i cut them up and sauté them with the other veggies, if Im using frozen, I toss them in when I throw the liquid in ( tomatoes, and broth).
After a few minutes, in goes the tomatoes and broth, can of drained and rinsed beans ( I prefer dark kidney. I like their taste, consistency and they hold up well in the soup by not turning to mush). I've also used garbanzo, or the white cannallini instead. At this time I like to put in some chopped okra. I like the taste and the way it thickens it up a bit too.
Let it simmer for a bit. Ill adjust the salt and pepper to my liking.
When the soup is about 15 or 20 minutes from being done, Ill toss in the diced potatoes. I dont like adding them too soon or the break up too much ( depending on the potato i have on hand). Sometimes ill actually precook the diced potatoes and just add them in last minute.
When the soup is 3 -5 minutes from being done, Ill add sliced zucchini. Honestly, this is my favorite vegetable in the soup. I slice them about 1/8 inch thick, throw them in and cover the pot. When the center of the zucchini ( where the seeds are , or should be) starts to get more transparent , then i know the soup is done. Almost kinda like al-dente. soft, but with a little bite to it.
If I want to make it more ' Minestrone -like', as they serve it in my local restaurant, Ill add a little cabbage ( not too much, or it dominates the flavor) and some noodles ( I prefer the small shells). Most the time I precook the pasta, and toss it in to individual bowls when serving, so i done wind up with a pot of HUGE shells ( especially if there is leftover the next day). It amazes me how much liquid those little boogers can absorb.
During the garden season, I may throw other things in it like spinach, chard, other beans that are ripe at the time, leeks.
Sometimes I may also add the rind of a parmesan cheese in it while cooking. To me, this totally takes it to the next level.
And as mentioned earlier, if i want it thicker , Ill save about 1/4 can of the beans, blend it up with some of the soup liquid , then pour it in towards the end. I dont like to make it too thick in the beginning, to avoid the risk of possible sticking to the bottom of the pan.