There is quite a bit to think about; consider whether the soup is thin or chunky, creamy or rich and the style of vegetables, fish or meat that have been used. Here are some quick tips.
Light thin soups, look toward the medium bodied whites, soft Beaujolais or light Italian styles.
Chunky & meaty soups, good soft, fruity reds from Chile or the South of France work well.
Creamy or fish soups, fuller flavoured whites such as lightly oaked Chardonnay or South African Chenin Blancs, Pinot Gris are worth a punt too.