Punish the takedown attempts and punish them hard. Knees on the shoot-in and clinches were already mentioned and that's a good start, but more can be done.
There were several times when Cain ended up on his knees or sprawled out on the mat after a failed takedown, and every time that happened JDS backed off and let Cain back to his feet to do it all over again. Instead, he needs to punch & knee him while he's down and keep hitting him as he tries to get back to his feet.
The next big one is staying the hell off the cage. There were several times where JDS backed himself right into the cage and then got clinched, dirty boxed, and taken down by Cain. The cage is not your friend, JDS needs to use more sideways movement to keep the center of the cage and stay off the fence as much as possible.
One more useful tool would be taking a page from the Chuck Liddell book and get comfortable with striking while backing up, and also striking with power while on the retreat. JDS, much like CroCop, is stuck on the defensive if you can pressure him and make him back up. He doesn't have the tools to counter that pressure and depends on retreating until he creates enough distance to reset and get back on the offensive. Fix that hole and JDS won't have to keep backing up so much, helps him stay off the fence and lets him start countering a lot faster.
Then there's general tightening up of the boxing game and better footwork to setup his punches. He needs to get out to the side more so he rip his punches in on better angles. I saw a few chances where he could've used the Mike Tyson shift
to really rip some punches in, but instead he backed straight off and tried to reset.