Were you able to clear chapter 3 of Deep Dive? If so, congrats! You can actually clear cube+. 

If not? Well, good thing for you. Cube+ is actually slightly easier than chapter 3 Deep dive. So you might be able to do it anyways! Hoorah!

Cube+ is quite literally just a harder regular operation cube. It features the original cube which was EN's first event, which already has guides for, and a second chapter! This time with 99% armoured enemies. Fun times. 

So in short, for cube+, bring an AR squad that can dish out some boss damage, and a few RF echelons or MG echelons. You also have the option of running bamboos for the bosses, but it's not needed. Nothing new is added aside from new bosses, but their mechanics don't change too much. 

Regular cube (chapter 1) already has a guide written for it. Look at that if you need more info on it. You also get a chance to get Groza once again if you didn't participate (or clear) the original cube!

ps because xecty wanted me to add this: All the bosses in 2-4, except for Ouroboros actually aren't tagged as bosses, so you can stun grenade them. Have fun!