Modals to express habits: WILL, WOULD, USED TO

Present

Would can express annoying habits which are typical of a person:

Tom would do something like that, wouldn't he? It's so typical of him!

Will is used to emphasise the characteristics of a person rather than describing the person himself or herself:

A friend will always help you. (this is one of the characteristics of a friend)

Past

USED TO

Used to refers to past habits and states which were true in the past but are not true any more. It can be used with both action verbs and state verbs:

On Sundays, my parents used to take me to dance school. (habit, action verb)
I used to hate dancing in those days. (state, state verb)

The negative and interrogative forms of used to are:

I didn't use to like dancing in those days.
Why did you use to hate dancing?

Used to + infinitive should not be confused with be/get used to + gerund (verb-ing):

She used to live alone in a small apartment. (it was true in the past, but not any more)
She was used to living alone in a small apartment. (she was accustomed to it)
She got used to living alone in a small apartment. (she became accustomed to it)

WOULD

Would describes repeated past actions but not states. It can only be used with action verbs:

From time to time, he would call her to ask if she wanted to meet for lunch.

USED TO or WOULD?

With action verbs, often either used to or would is possible:

On Sundays, my parents used to take me to dance school.
On Sundays, my parents would take me to dance school.

With state verbs, however, only used to is possible:

I used to hate dancing in those days.
I would hate dancing in those days.