Many of the rules for freezing soup basically simmer down (...pun intended!) to holding back the ingredients that won't freeze well and then adding them back in when you reheat the soup later. If you're making some soup to eat now and some to freeze, just scoop out the portion you want to freeze before adding these final ingredients.
1. Hold Back the Cream: Cream and milk tend to separate and become grainy if frozen. It's easy enough to freeze the soup without this ingredient and stir it in while re-heating. Non-dairy milks like soy milk and coconut milk theoretically freeze better, but I still find the soup is best when they are added later.
2. Hold Back the Pasta: Pasta turns to mush after freezing. Completely unappetizing. It's much better to boil fresh pasta and add this directly to the reheated soup.
3. Hold Back Any Ingredients Added in the Last 5 Minutes: Ingredients like fresh herbs and eggs tend to be very delicate, which is why they're added so late in the game. This makes it likely that they won't stand up well to being frozen and will taste better if added fresh. (The exception to this that I come across most frequently is canned beans, which do fine when frozen.)
4. Slightly Undercook Vegetables: The vegetables will cook a little more when the soup is reheating, so freezing while they're still slightly underdone prevents vegetables from turning to mush later on. This is an especially good tip to remember with potatoes. Again, if you're making some soup to eat now and some to freeze, scoop out the portion you plan of freezing before finishing the soup you plan to eat.
5. Freeze Small Portions: Smaller portions are quicker to warm up for a weeknight meal and easier to arrange in a crowded freezer.
Soups That Freeze Best: Bean soups, vegetable soups, broth-based soups, soups with brown rice or wild rice, pureed soups, beef and chicken soups.
On a final note, remember to date and label all your containers of soup. Soups tend to all look the same once frozen, so you'll be glad you did!
What other tips do you have for freezing soups?