What is the difference between think of and think about?

[Karina]

Think of/about

Does anyone know when you use one or the other? Is there a rule? I can think of examples where I can use them properly but my students want a rule and I don't know any.
Can anybody help????

I don't think much of this.
I think about this problem constantly

[Lucy]

Dear Karina,

Think of is usually used when giving an opinion; eg "what did you think of the film?".

Think about is usually used to mean consider,etc. Eg "what are you thinking about"; meaning what is going through your mind right now.

Kind regards,

Lucy