really
personally
I personally think it's all been a lot of fuss over nothing.

honestly, seriously
Did you honestly think I would agree to that?

never, sometimes
I never thought you would carry out your threat.

differently, otherwise
That's my opinion, but you might think otherwise.

be inclined to
I'm inclined to think we've been a little harsh on her.

about
I still don't know what he really thinks about it.

of
What did you think of the movie?

suddenly

of
I suddenly thought of a way I could help.

carefully, deeply, hard, long and hard, seriously
She thought long and hard before accepting his offer.

fast
clearly, rationally
He seemed to have lost the ability to think rationally.

frantically
What can I do now? he thought frantically.

bitterly, dully, glumly, grimly, irritably, miserably
ruefully, wistfully, wryly
again
You really should think again about that.

twice
You should think twice about employing someone you've never met.

dread to, hate to, shudder to
I hate to think what would have happened if we hadn't arrived.

about
Think about what you are going to do next.

of
I often think of Jane.

not think straight
The drugs were affecting her and she couldn't think straight.

think big
You need to think big if you want to run this business.

Think is used with these nouns as the subject:
expert, observer, researcher, sceptic

Think is used with these nouns as the object:
thought, worst