See below. Sometimes the source can be the cause: canned veggies typically are less appetizing than fresh or frozen. Trying different forms of preparation may help: steam/bake/fry/grill/ add to casserole or stew. Avoid letting other family members complain about veggies; picky eaters often pick up their habits from other family members, especially parents.
Kid or adult? Any vegetable can be pureed into tomato sauce and served over spaghetti! kids and adults like to dip fresh vegetable pieces into hummus or greek yogurt dips. You can always add vegetables by stirring them into soups (just watch the sodium intake) or vegetable pizzas. Don't forget about low-salt vegetable juice. A child will often try something they've prepared. Get them cooking! good luck.