I lived vs I used to live

Solution 1:

There is no difference between the two. Both mean the same.

Solution 2:

They're not quite the same. Used to carries an extra Presupposition about the present, to the effect that if X used to VP in the past, then it is presupposed that X no longer VPs.

• I lived in Prague 5 years ago and I've lived in Prague ever since.
• *I used to live in Prague 5 years ago and I've lived in Prague ever since.

This can lead to interesting interactions with other presupposition triggers; for instance,

• Carter used to be President.

asserts that he was President in the past and presupposes that he's not President now, whereas

• Carter isn't President any more.

asserts that he's not President now, and presupposes that he was President in the past.

Since only assertions but not presuppositions can be negated, if someone were to say one of these sentences about President Carter and you said they were wrong, what would you mean?

• In the case of the first sentence, if they're wrong in saying that he used to be President, then you're claiming he was never President.

• In the case of the second sentence, if they're wrong in saying that he is not President any more, then you're claiming he's still President.

As ruakh points out, the stative nature of the verb live makes the durative used to unnecessary, but the real weirdness is the extra and probably unnecessary presupposition.

Solution 3:

Used to refers to a state or habit in the past, whereas the past tense describes an event at a particular time in the past. That means that the first sentence would be unlikely because a state or habit cannot normally have such a specific time reference. I used to live in Prague on its own is fine, but if you wanted to specify when you lived there, then the second sentence is what you’d use.