USE
4. USED TO or PAST SIMPLE
We use "used to" if we want to emphasise that something was true in the past and is not true any more. If it is not important, we may use Past Simple with no big difference in meaning.
Compare:
I played chess when I was a child.
(Just a fact about me.)
I used to play chess when I was a child.
(It is also a fact about me. The difference is that I want to emphasise that I played chess when I was a child but I do not play chess now.)
5. PAST SIMPLE NOT USED TO
We use Past Simple instead of "used to"
a) for single or not regular actions in the past
She had a driving lesson last week.
b) for repeated actions in the past with a number
She had driving lessons three times last week.
c) to talk about a period of time with "for"
She had driving lessons for six months.
(NOT: She used to have …)
6. USED TO and PAST CONTINUOUS
We use "used to" to talk about a regular action in the past that does not happen any more. We use Past Continuous to talk about the action that was in progress when the other action happened and about the action that was happening at a stated time in the past.
Compare:
I used to read a lot.
(I read regularly in the past, but I no longer do this.)
I was reading when my friend came.
(I was in the middle of reading when my friend came.)