I agree with Jessacita- unless you're making a slow-cooking soup that allows all the flavors to meld for a while (heck, even in these i don't use water), use broth. Also, start with sauteeing some flavorful veggies, such as mirepoix. And add fresh herbs toward the end- it adds so much!

It's the classic french combination of 2 parts chopped onion to one part each chopped celery and carrot. Maybe i spelled it wrong. Other ethnicities use bell pepper instead of carrot or garlic and ginger.

Maybe roast your vegetables before you add them? Adding coconut milk makes soups very rich.

Brainstorming... :)

i agree w/ lindsay...saute the 3 standard veggies up first, just to soften.
you can add a bit of wine to this saute too. white for clearer broths (or potato, squash)  or red for tomato based orbeans, lentils, etc. if you add it at this point, the alcohol burns off...i fyou add it later, when the other liquid is simmering, there is a more pronounced flavor, which you may or may not like. imo, sometimes it can be really strong.

garlic!! even if you only use a bit, it adds more depth to soups. or
roast your garlic before hand.

a tablespoon or two of tomato paste is esp good w/ beans, lentil, italien minestrone-type soups(even if it a "white" broth based soup).
if you add tomatoes to your soup, you can also use fire roasted canned.
adding a bit of balsamic or red wine vinegar to "red" soups gives it some more tang. and a tablespoon or two of maple syrup helps counteract the acidity in tomatoes..it reallly brings out the flavors.

roasting squash for squash soup.
roasted red peppers (they are sweet, not spicy)
a dash or two of tabasco. or red pepper flakes...just a dash or two makes a big diff!

lots of herbs! i always taste towards the end and "doctor" it up.... adding extra dried herbs and powdered garlic or onion as needed.

what spices do you add? do you add enough salt?

My spice knowledge is sadly, sadly lacking. I never really know what spice/herb will compliment what food, so I tend to be shy about using them.  As for salt, I don't tend to add it because I find using broth makes it salty enough.

i's say definitely do onions, garlic, pepper... and maybe at least a little salt. then i would say concentrate on one thing(it doesn't really matter what because the soup you are making sounds versatile).. for instance italian which you can buy premade 'italian seasoning'...

i actually have a crap knowledge of spice, too, and i am trying to get better. i would suggest getting a good cook book. even non-vegan ones tend to have a section on vegetables and spice counterparts as well as what types of spices go well together.

Saute onion and garlic in olive oil (doesn't have to be EVOO), throw in a bay leaf and a pinch of thyme.
Use a little (like half a cup) of white wine in conjunction with the broth.
Stir in a little Marmite; it's salty so you won't need a lot of extra salt.
I use dill a lot, but that's just me. Some people don't like it in soup.
At the table, stir a small spoonful of miso into your serving, if you like. Also kind of salty--the dark is much saltier than the light colured miso.
Get one of those salt grinders with a mixture of herbs or peppers in, and grind a bit on your serving. I have two, one contains a bit of salt and provencal herbs (thyme, rosemary, tarragon and dried lemon peel) and the other contains oregano, garlic, salt and chilli flakes. I use the oregano one more often.