For starters, let me just say that the disdain directed at new (and important) innovations in sport jiu jitsu is always puzzling to me. In these contexts the common complaints are that that these innovations are (a) "bad for the sport," (b) wouldn't work in "real world" situations, and (c) are tantamount to nothing more than stalling techniques. While there are other grumblings, these are the most often heard--and they should each be ignored. Jiu jitsu is an ever evolving martial art that takes many forms and has varied purposes (depending on both the practicioner and the context). Innovation is always a good thing in jiu jitsu as in anything else.
As far as I can tell, the driving force behind the dismissive misgivings directed at innovators like Keenan Cornelius, the Miyao Brothers, the Mendes brothers, and others is laziness more than anything else. Traditionalists are inconvenienced by the fact that their old school techniques have to be modified and refined to "get around" the new developments in the art. Rather than dedicating their time to finding the work arounds as Rodolfo Vieira has done, some people prefer instead to bitch and moan about the new techniques on internet forums and grappling blogs--which is far easier than learning both how to use and avoid the new techniques. This latter approach is both petty and small-minded. It's also an attitude lamentably fueled by some of the old guard in jiu jitsu. Take, for instance, all the famous grapplers who said disparraging things about the 50/50 when it was the target of ridicule de jour. If enough Gracies and other legends of the sport say something's garbage, it has to be true, right? No. Indeed, the more grumbling about the technique, the more likely it is that there something to it!
That's not to say that beginners should jump on every grappling bandwagon that comes along--especially when they should be focusing instead on the basics. But when a new black belt like Keenan Cornelius is able to succesfully use a technique against some of the best grapplers on the planet, the technique should be taken seriously and innovators like Cornelius should be given praise rather than ridicule. If the worm guard was as laughable as some suggest, why does it work at the highest levels? So, rather than sneering from the sidelines, roll up your sleeves and dedicate yourself to figuring out the principles of how to use and shut down the worm guard (especially if you're an upper belt). The effort will always be worth it whenever new techniques come down the line. To think otherwise is to have grappling feet of clay. That may have worked for the old school players, but it won't save you from the white belt at your gym who isn't as stymied by tradition. He'll stick you in the worm guard and you'll rue the day you decided to complain about the technique rather than trying to figure it out. Or so it seems to me.
That said, here are two videos that I found especially helpful. The first is a nearly 20 minute "study" by Jason Scully. The second is a video that contains instructional concerning several entrances to the worm guard from the more common leg lasso position. So, as always, watch, learn, and go train.
p.s. Cornelius also has some helpful instructional videos posted on the beta version of his training cite. At $10 per month, it's a good deal. He has lots of good stuff posted already!