May I? ～てもいいですか？

Asking permission and Being polite go hand in hand. Here is how you do both in Japanese.

Construction:　
Take the て form of a verb
Add もいいですか？

電話を使ってもいいですか？
denwa o tsukattemo ii desu ka?
May I use the phone?

休んでもいいですか？
yasundemo ii desu ka?
May I take a break? (from work, from studying, etc)

ちょっと話してもいいですか？
chotto hanashitemo ii desu ka?
May I say something? (I'd like to speak a little)