AffirmativeA declarative sentence indicating "yes"; also called a positive sentence. E.g.: John likes squash a lot. forms

Used to and would are both used for past habits. There is, however, a difference between the two. Would describes repeated actionA general term expressing that somebody or something does somethings, but not stateA condition that exists at a particular time. E.g.: I am sick. This melon weighs two kilos. s, while used to can refer to both repeated actions and states.

On Sundays my parents would always take me to dance school.
I used to hate dancing in those days.

Compare these two sentences:

From time to time he would get up and glance critically over his work and look at his models.
I would like to go home.

The second sentence cannot refer to past time as the verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis. like expresses a state, not an action. Therefore it cannot express a past habit but only a present state. For the very same reason the following sentence is incorrect:

While at school he would be the smartest kid in the class.

Instead of would you need to use used to:

While at school he used to be the smartest kid in the class.

NegativeA declarative sentence indicating "no". E.g.: Tim has no friends. and interrogativeThe sentence type used to express a direct question. E.g.: What are you doing? forms

As used in the structureThe way in which the parts of a sentence, clause or expression are arranged. E.g.: make somebody + infinitive in "The teacher made me rewrite the composition." used to is a main verbA verb that can express an action or state in itself. E.g.: John likes squash a lot. ("like") in the past simple tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses., the interrogative and negative forms are:

Did he use to be the smartest kid?
While at school he didn't use to be the smartest kid in the class.

Present simple to express past
Past time Revision questions: past time