The two most common prepositions used after the verb "think" are "about" and "of." They are very similar, but there is a small difference.

Usually when you think of something, it is a brief moment - just a few seconds. It is also used for opinions. When you think about something, you are considering it for a longer time - like a few minutes or more.

Every time I hear this song, I think of my mother.

(thinking for a few seconds)

What do you think of my new haircut?

(opinion)

I'm thinking about moving to a different city.

(considering)

I still get angry when I think about all the rude things my sister said to me. (thinking for a few minutes or more)

Common error: Don't use "think to" for "considering."

I'm thinking to do an intensive English course in Canada.

I'm thinking about doing an intensive English course in Canada.

Fact
The most expensive painting ever sold at auction was Portrait of Dr. Gachet by Vincent van Gogh. On May 15, 1990, Ryoei Saito paid $75 million for it. He followed up that spending spree by paying the second-highest price ever, $71 million for Au Moulin de la Galette by Pierre Auguste Renoir, just two days later.      .. More >>