Delay, Deny, Defend
Don't let them have a smart phone until high school. Do not allow unlimited use. Do not allow certain apps. No phones in room at night. Continually have to "defend" and argue about it.
How are they going to learn how to control themselves when you're not around though?
Just because you're strict in one area doesn't mean that you're completely mistrusting everything. You can (and should) still teach responsibility in the same way that generations have before social media.