If you have this problem, wash your hair daily with a mild shampoo that does not contain conditioners -- often labeled "clarifying"; these will leave the least amount of residue.
Then use a light creme rinse or conditioner only on the ends of your hair, if needed, and be sure to rinse thoroughly.
Avoid all products containing silicone , oils or lanolin, as well as two-in-one products.
During the day, a quick combing can help redistribute oils and reduce that stringy appearance. Or, for more a more serious case, spritz a little water on your hair and blow-dry it using a comb to remove and redistribute oils -- the heat of the dryer will make the oils more liquid and easier to manipulate.