Adding starch, such as flour or cornstarch, to the soup is the easiest way to thicken it. Combine 1 to 2 tablespoons of the starch with equal cold water and whisk until it forms a paste. Then slowly add this mixture to the soup until it reaches your desired thickness. Another option is to puree some cooked beans and add them to the soup. This will thicken the broth without changing its flavor too much. You can also thicken the soup by cooking it down on low heat for longer than usual, allowing some liquid to evaporate until it reaches your desired consistency.