Sending Nudes?

Hi so I've never sent nudes or any kind of picture in lingerie before. It's just never been something I was comfortable with. I'm currently in an LDR and I know my boyfriend is really missing the whole physical part of our relationship (I am too!). We've never sent nudes or even sexted but he asked about nudes once a while ago and I said no. So I know he'd like them but I guess I'm just not very sure about the rules that go with nudes? Do I have to warn him first- I don't want him opening it around friends or anything like that? Are there things you should or shouldn't do? What do guys like with nudes? 
I want to keep our sex life alive as much as possible (we don't see eachother often at all) but I'm just so naive about this stuff. We're both legal and I trust him so that's not an issue at all. Any advice would be great! Thank you