How to resfue?

In our daily life.sometimes,we have to refuse people's requirements and other questions when the things are out of our scope,or ability,or bottom line.

So when we meet these situations,how should we do??I think first.we shall think ourselves to check the result if we do it.and then,we can explain to friends how the disadvantage and danger of these matter and help them to find more effective solutions.

If we do like this,I think friends or others will release our status,also we will have a better relationship between people.