Preplan these:
2 body bags into the toilets,
{{With the addition of Jack of All Trades, the aced variant allows heisters to carry a body bag case with them instead, along with 2 ECMs as per usual.}}
Unlocked doors and cage doors to cut the cracking time for the personnel doors,
Position the guitar case to the smoking area closer to the entrance of the casino,
Disable metal detectors,
Spotter at the smoking area,
Heartbreaker Annie to lock the red code number in position of the VIP section, and
A vault gate keychain for the gates in the vault.

Serious Note: The Spycams in the heist are really bad at spotting guards. They're either blocked by something in their view or have just a tiny field of view.

First things first, go into the casino's employees area without your gear and locate each and every room's position, most importantly the Archives, Server Room, and the Locker Room. Remember where they are. If you can't remember all of them, just remember the Archives for now.

Now go collect your gear from the guitar case and put on your mask. Be cautious even when you're taking your gear, as a guard may be present nearby. Take the sleeping gas with you.

I highly suggest searching for the three color code numbers as soon as possible. Start with the red one, as it's the closest to you. Crawl your way to the back of the drinks bar inside the VIP section and avoid being seen by the civilians and cameras. You should be able to open the briefcase while crouching behind the bar, but to see that number, you need to make a quick stand-up-and-crouch.

Next, head for the employees area and enter the Manager's Office. You should find a lootable painting and a safe behind it. Open it, preferably with aced Nimble, and obtain the blue code number. Stash that painting into the van in the Delivery Room.

Finally, enter the Locker Room cautiously. In there are a couple of cameras and a guard. You should be able to find the green code number in one of the many lockers. Keep an eye on the guard, as he may spot you while you're picking on most of these lockers. Now unless you're going to go loud, you should ignore the armory.

Remember these three color code numbers. You should, even though Bain would repeat the code once you've reached the vault's keypad. Keep in mind that the blue and green color code numbers tend to switch code positions every heist. Sometimes blue is the second number, sometimes green.

Side Note: You can do this much later, after disabling the vault lasers guarding the vault entrance.

Now, make your way to the Archives carefully, as guards are plentiful and have eagle eyes. I suggest using the pool area or smoking area as a path, as inside the casino are full of civilians playing casino games and sometimes guards as they walk in and out. As you enter the employees area of the casino, watch out for cameras and guards.

Now when you enter the Archives, there usually would be three cameras clustered in the room along with a civilian. You should find the blueprints in one of the bookshelves. Of all the bookshelves, only one is going to be impossible to search without the use of a Camera Loop or an ECM. The rest either have no cameras directly disturbing you or just have some angled position that you can hide from the cameras while they're being searched.

Once you got the blueprints, head for the Server Room. Find a poker-chip-themed USB stick and grab it. Go ahead to scan and fax the blueprints to Bain. Now make your way to the Reception and stick that USB stick into a computer there. Beware the receptionists on the left and right doors, as they may see you or the computer being used. Once done, grab that USB stick and head back to the Server Room and stick that USB stick into any of the laptops. Wait for a while to see who you're looking for on the big screen in the Server Room. It'll be a man, either in a white shirt or purple shirt.

When you find him near the slots residing by the toilets, identify the drink he consumes and match it with the one you're going to find. Even if you don't remember it, Bain will tell you what drink you're looking for. Grab that drink and pour it into the glass of the target. Once again, mind the guards and civilians while doing this.

Once he's spiked, allow him the make his way to the pool area or smoking area so you can grab his room card. It is highly suggested you kill him and hide his body. Tying him up makes him suspectible to being spotted by wandering guards.

As you grab the room card, keep your ears open for Bain's info on which room the card should be used for, as he will only say it once. Missing this info can be a critical error as you have only one room card to use. You don't really lose the card, it's just that he doesn't mention the number again, so the only loss is time. Once in the correct room, using that sleeping gas on the vent in the room should cause all the guards in the Security Center to sleep. Doing this will also disable cameras.

Make your way to the Security Center and hack the computer inside to disable the lasers that guard the vault entrance. Make no attempt to damage the guards inside. Better to let them sleep than to waste pagers. At this point, you should keep an eye out for guards who wander nearby outside the Security Center as they will be alarmed when they see these doors opened. This is where the pagers should only be used; on guards who wander around in the employees area.

Interesting Note: You can use the elevators as hiding spots, in case you find yourself feeling tight. Simply press the elevator buttons to open it, step in, and press the buttons inside to close the doors. Use of Sixth Sense can help here, since you can't see the other side when inside the elevators. These elevators can be found in the employees area and the hotel area. Contrary to popular belief, these particular elevators don't go up or down.

The vault has a "Private" door containing the Dentist's Loot, 3 vault gates that guard bags of cash and a staircase leading upstairs to a motherload of cash; loose bundles and bags of it.

When the lasers are down, enter the code into the vault's keypad. Get in and place a drill on the "Private" door before using the vault gate keychain to open all the gates in the vault. Loot the cash to your heart's content. Once the "Private" door opens, mind the lasers that guard that Dentist's Loot.

Now, carry all that loot to the elevator in the middle of the Security Center. Place them properly on the elevator or they will fall off once you're ready to lift them up. Now stash the loot, primarily the Dentist's Loot, to the van in the Delivery Room. Final warning: Mind the guards. Now escape when you're done.

Other Loot: There's a stash of poker chips in the guitar case. There may be stashes of poker chips and loose bundles of cash in the Reception; in cabinets and on tables, and in the Locker Room's lockers. There may be jewelry, stashes of poker chips and loose bundles of cash in the hotel rooms. There's a rare chance of you winning at the slot machines, if you play them, with the reward being a winning slip.