Thinking

Consistency is the key.

- I was thinking about something today.
- What were you thinking about?

- I thought about something today.
- What did you think about?

Did you cry yesterday? and Were you crying yesterday? What is the difference between these?

There can be a difference.

Did you cry yesterday? At any time yesterday, did you cry?
Were you crying yesterday? When I came into your room yesterday, and your face was buried in your pillow, were you crying?

Context usually makes it clear.

But what if someone told me today that they were going to cry? What do I ask them tomorrow? Did you cry or were you crying?

What do you mean? That somebody was about to cry?

AnonymousBut what if someone told me today that they were going to cry? What do I ask them tomorrow? Did you cry or were you crying?

Did you cry yesterday?

Would 'were you crying' be incorrect?

I was thinking about something.
What were you thinking about? - Would 'what did you think about'be incorrect?

AnonymousWould 'were you crying' be incorrect?

Not incorrect, but just weird. This question seems to refer to a specific duration of crying. You just want to know whether the person cried or not.

AnonymousI was thinking about something.
What were you thinking about? - Would 'what did you think about'be incorrect?

Aspara GusNo, just inconsistent.

So, native speakers don't do that?

Also, what's the difference between:

I cried yesterday.
I was crying yesterday.

AnonymousSo, native speakers don't do that?

Some may. I wouldn't.

Anonymous
Also, what's the difference between:
I cried yesterday.
I was crying yesterday.

Context!