Simmer uncovered to reduce excess liquid
Mash some of the potatoes, beans, or vegetables in the stew
Stir in a slurry of cornstarch and cold water
Stir in a slurry of flour and cold water
Add a beurre manié of equal parts soft butter and flour
Mix in tomato paste
Add instant mashed potato flakes
Stir in a small amount of arrowroot mixed with cold water
Add a roux made separately from butter and flour
Purée a portion of the stew and stir it back in
Add bread crumbs
Add crushed crackers
Add grated cheese if appropriate for the stew
Let the stew rest briefly after cooking to thicken naturally