When I was in basic training SSGT M., our drill sergeant, made sure we would always button or zip our BDU pockets or rucksacks close. He was very serious about it. He would make our lives miserable if he'd find one of us with a trouser pocket unbuttoned or one of the rucksacks compartments unzipped. We would run forever, go down for pushups until our hands bleed. There was no way we would forget to button that pocket flap. At that time I didn't understand why he was so maniacal about this.
When we finished boot camp and moved to advanced training, he moved with us and became our platoon Sergeant. We could talk to him then and so we asked him the reason behind his obsession with the pockets. He replied:
When you are in combat, running, jumping, shooting back and relying on your gear, you don't want to find out when you life depends on it that your SERE kit is gone because you left that trouser's pocket open, or your blowout kit or the compass on the ruck's pouch or the rifle's magazine... No, you want to make sure you have them when you need them. That's why I am making sure you have it. By forcing you to close those pockets and making it second nature to you, you will always have your gear with you. Well, unless it got blown, in which case that button will be the last of your worries.
That was 20 years ago. Even today I close all my pockets automatically. It stayed with me. It saved me in more than one occasion when in combat, climbing, or even on physical pentests. By closing those pockets I make sure my gear is secure.
The same applies to other things. Pay attention to details, get your gear ready and practice, practice, practice. Make the use of each piece of gear second nature, learn each piece of gear, each of its features and how to use them as if your life depended on it, it might one day. Choose the simplest and most reliable gear, even if it's a bit more expensive. Under stress, when you really it need, it won't let you down.
Now, translate this to planning, preparation and execution. Be meticulous about little details, be maniacal about each an every aspect of the planning and the operation. Even the less than sexy parts of it. It's the small details that can ruin the operation.
Keep your pockets closed.