How to Be Polite in English

Could/Would you please...?

If you don't mind, ...?

If it's not a problem, ...?

When you have/get a moment/second, ...?

If/When you get a chance, ...?

By any chance, ...?

I'd appreciated it if you would ... (only for people in authority)

What if ... ?

How about if ...?

What do you think about ...?

You should probably ...

I don't want to keep you, but/so...