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.
As Vallabhbhai wished to become a barrister, he was saving money and making preparations to go to England. He wrote a letter to a travel agency about his trip to England. By chance it fell into the hands of Vithalbhai. He told Vallabhbhai, I shall go to England first; you can go later. Without the slightest hesitation Vallabhbhai agreed. Take it that my money and my ticket are yours. Make use of them gladly. And if you need money in England write to me. I shall send you the money, he told his brother. Vithalbhais wife was not a woman who would easily adopt herself to circumstances. She was worded; what was she to do if her husband went abroad? Who would look after her? Vallabhbhai said, Come and stay with us till my brother returns. Think of my house as yours.Three years passed, and the elder brother returned from England.