Asking permission

May I…?
Do you mind if I…?
Could I…?
Is it all right if I…?
Do you think I could…?

Sure, go ahead.
By all means.
No, I’m afraid you can’t, because…
I’m sorry but…
Agreeing and disagreeing

If you want to agree with someone you can say:

That’s exactly what I think.
That’s a good point.
Quite right, I couldn’t agree more.
That’s just what I was thinking.
I agree entirely.
Yes, I’m all in favour of that.

It’s often considered rude or aggressive to say “You’re wrong” or “I don’t agree with you”. It’s more polite to disagree with someone by saying.

I see what you mean, but…
I don’t think it’s such a good idea…
That’s true, but on the other hand…
I don’t quite agree because…
Maybe, but don’t you think…?

If you require some information you can say:

Could you tell me if/when/how much/why…?
I wonder if you could tell me…?
I’d like to know…
I’d like some information about…

Or you can write:

We require the following information…
Please let us know whether/when/how much…