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?
I'm thinking about moving to a different city.
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.