I don't think

1. I disbelieve
2. A warning that what was said was ironical (informal)

I shouldn't (or wouldn't) think of

I would not under any conditions

just think of it or to think of it

An expression of surprise, disapproval, longing, etc

put on one's thinking-cap

To devote some time to thinking about some problem

think again

To (be forced to) change one's opinion

think aloud

To utter one's thoughts unintentionally

think back to

To bring to one's mind the memory of (a past event, etc)

think better of

1. To change one's mind about (doing something) on reflection
2. To feel more approval for

think for (archaic)

To expect

think little (or much, well) of

To have a poor (or high) opinion of

think long (archaic)

1. To yearn
2. To weary (from deferred hopes or boredom)

think nothing of

1. Not to consider difficult, exceptional, etc
2. Not to hesitate in (doing)

think nothing of it

It does not matter, it is not important

think on one's feet

To solve problems as they arise during an activity

think out

1. To devise, project completely
2. To solve by a process of thought

think over

To reconsider at leisure

think shame

To be ashamed

think through

1. To solve by a process of thought
2. To project and consider all the possible consequences, problems, etc relating to (some course of action)

think twice

1. (often with about) to hesitate (before doing something)
2. To decide not to do something

think up

To find by thinking, devise or concoct