It's all about comfort! You just have to tell the girl that you don't care if she does or doesn't send you nudes. It's all about making the interaction between the two of you grow sexually in order to create steaming emotions of lust inside one another. Also, trade them over snapchat vs. texting or kik, because studies have shown that girls have been more willing to send nude photos when on snapchat because these photos "disappear". Which ties right back into the idea of comfort. That's all the girl want to feel in order to know that she can trust you with these pictures.

So let's recap: 1) Comfort, comfort, comfort -this means take her feelings into account -this means don't continuously demand without having given any value of your own. -means tell her flat out how you feel, and how you want her to feel. -never apologize for expressing your sexuality.

2) Don't share them. Girls talk and that's a bad reputation right there.

3) Only ask girls you truly want nudes from. Nothing is sadder than a man who begs to those who don't have what he needs.

4) Have fun! The biggest problem with guys and girls these days is that we take ourselves too seriously! Learn to let loose and she'll follow (it's that comfort thing). Learn to laugh off the no's and learn to embrace the yes's!

Now go out there and have some fun, you titty loving horndogs!

TL;DR: Make girls feel comfortable with you in order for them to send nudes. Have fun while doing it, or what's the point!