The NOD Command Center
After the Defense Facility, this is to me the most importnat structure to protect. Without it, you cannot send your units out to attack. It is also directly responsible for setting the maximum level of the attack units. This means, if you Command Center is level 30, your army units cannot be upgraded beyond level 30. Obviously, the higher the level the better. This should be upgraded regularly; it also becomes quite expensive so do it first after a blitz.The Command Center should be given the third safest spot in your base. You'll thank me later when you've endured one attack and can retaliate with that same base instead of using another one. I'll also say though, that it is NOT needed in every base. For example a credit base may only have defense, no need to attack, you're much better off concentrating your firepower instead.
Next to the Construction Yard, the Defense Facility is the most important base structure. It is responsible for rebuilding your base during and after a raid. There is a halt before you can start rebuilding your base so if your opponent runs out of CP, wait a few minutes and you will be able to repair. The same is true if you take our your attacker's base before they take yours out first. You can use another base to attack your assailant, try and do'em in in one hit. Taking out this structure means you cannot repair your defense units. This structure will need to be repaired if it was heavily damaged. It's not an impossible task, it just demands a lot of focus and have an excellent timing.
Keep in mind to keep this unit equal or higher than you defense structures as you might not get the full 70% repair after an attack. The game has it that after an attack, you base will auto-repair immediately after the attack. If you Repair Facility is left unscathed, it will repair 70% but if it got damaged down to 50% let's say, you will only repair 35%.
