A ‣ Asking someone for their opinion 
What do you think of his new book / Tom’s girlfriend? (asking about a specific thing or person)
What do you think about global warming / cosmetic surgery? (asking about a general topic)
How do you feel about working with the others?
B ‣ Introducing your own opinion 
Personally, I think Helena was probably right.
Personally, I feel that we should increase the price.
In my opinion [I think], we need to change the direction of the company.
My view/feeling is [my opinion is] that we need to wait a bit longer.
Common mistakes
Personally, I don’t think it’s a good idea. (NOT I think it’s not a good idea.)
In my opinion, motorbikes are dangerous. (NOT On my opinion OR In my meaning)
In most situations, it is probably easier and more natural to use personally.
C ‣ Giving the opinion of others 
The newspaper says that his death was not an accident. (NOT It’s written in the newspaper)
According to the paper [the paper says], the government didn’t know about it.
D ‣ Agreeing and disagreeing (with someone) 
I totally agree (with you) [agree completely, 100%].
I partly agree (with you) [agree but not completely].
I agree (with you) to a certain extent [partly agree].
Common mistakes
I agree with you. (NOT I’m agree with you.)
Do you agree? (NOT Are you agree?)
In British English, it is common to agree with someone before giving a different opinion.
That’s true, but I think …
I see what you mean, [I understand what you are saying] but …
I agree to some extent, but…
I think that’s a good point [idea or opinion], but…
I take your point [I understand and partly agree with your opinion], but...
E ‣ Giving a strong opinion 
I feel very strongly about military service. I think everyone should do it.
I think you’re absolutely right / wrong [100% correct/wrong].
I don’t agree at all [I completely disagree].
I disagree completely [100% don’t agree].