Lately I've had a string of rib related BJJ injuries, be it a popped rib or bruised rib. What advice can you all offer to help avoid these? I've already decided to play open, rather than a closed guard, to avoid getting stacked. Are there specific warmups, techniques, exercises (working the abs before rolling), drills, etc. that you have had success with? I have found the general warmup at my school severely lacking in this regard. 
Abs homie. And intercostals, serratus transversus abdominal etc.
Your ability to create intrathorassic pressure is paramount to not busting up your ribs. And by that I mean keeping your mid section tight with musculature and breath.
Sometimes when you're tired you stop keeping your midline tight And someone's weight will collapse your structure leaving your ribs at risk.
For one, when I've got some mountain if human putting the pressure on I think of maintaining my midline structure and not twisting under the weight. If your hips are pointing a different direction than your shoulders, your ribs are in trouble. Counter rotation=potential badness.
So in part, it's strengthening your body, and in part it's a technique unto itself.
Hope that helps.
I've cracked ribs on my left side before and just last week tore my intercostals on my right side trying to get up out of knee on belly. It was a bad idea, now I get to sit on the sidelines for a couple weeks.
omoplautistic - Abs homie. And intercostals, serratus transversus abdominal etc.Voted up: good advice, especially the tip on the breath. Also, I've been slacking on the abs for several months, but hadn't drawn the connection between recent injuries less ab work. Also, I'm going to arrive to class early from now on, and work all areas to warm them up completely.
Your ability to create intrathorassic pressure is paramount to not busting up your ribs. And by that I mean keeping your mid section tight with musculature and breath.
Sometimes when you're tired you stop keeping your midline tight And someone's weight will collapse your structure leaving your ribs at risk.
For one, when I've got some mountain if human putting the pressure on I think of maintaining my midline structure and not twisting under the weight. If your hips are pointing a different direction than your shoulders, your ribs are in trouble. Counter rotation=potential badness.
So in part, it's strengthening your body, and in part it's a technique unto itself.
Hope that helps.
BTW: I've been icing them 3x per day, taking Advil, and using a DMSO/ MSM product called Penetrex. I appear to be recovering much faster this time around.
Are you giving yourself enough time to heal? Rib injuries are very easy to reinjure. 
In for tips, just did mine yesterday. :(
Omoplautistic-Counter rotation=Potential badness....You sir, are right on the money!!
BJJWRESTLER - Omoplautistic-Counter rotation=Potential badness....You sir, are right on the money!!Woot!
In other news, if you want to make a guard pass easier, create counter rotation in your opponent! Ta-daa! You've just made them weaker!
Oh, also, keep your head in line with your shoulders when under pressure to protect your neck, and when in doubt, ball up!