The best thing that I can recommend doing, is to have good mobile versions of your sites. This is the most important part of equation, as of late 2014, and people completely omit it, still.
If you want to stay in this business, you need to work hand in hand, with programs like
Bitter Strawberry, and
Sex Goes Mobile. Mobile popunders from
Plugrush, are very important part of the mix too.
There is more networks like this, but they are less popular. When you get to the level of high traffic xxx sites, give a try to
First Mobile Cash, and
VPS Mobile, and they may turn out even more profitable, for some of your sites.