If you want to agree with someone you can say：
-That's exactly what I think.
-That's just what I was thinking.
-In my opinion， office workers are not paid well enough.
-That's a good point.
-I agree entirely.
If you want to disagree with someone：
-Quite right， I couldn't agree more.
-Yes， I'm all in favour of that.
-Well， my opinion for what it's worth……
-I can see what you mean， but ……
-I don't think so， because……
-I don't think it's a good idea……
-Maybe， but don't you think……？
-That's true， but on the other hand……