Enter the offices through the last Hoover Dam tower.
Install the override chip into the large, multi-screened terminal; choose to either activate the Securitron Army beneath Fortification Hillor deactivate the dam's power output, rendering it useless to the NCR.
On the same floor, go southeast past the second tower exit (with the kitchen) and open the door to Hoover Dam Power Plant 1. It opens to a balcony with the switch; flip it to power the east power plant on the western wall.
Go back topside to deal with the Legion and NCR on the eastern side of the dam.
Enter the Legate's camp to deal with the Legate, either by killing him or convincing him to surrender with Speech and Barter checks of 55, 65, 75, 85 and 100.
Return to the camp entrance and deal with General Oliver, either by killing him and his entourage of six veteran rangers or convincing him to surrender with two Speech checks, one of 50 and another of 100.
Go to the Control Room in Hoover Dam and install the override chip.
Activate the eastern power plant to power the Securitron Army.
Using Boone as a companion while pursuing the dream of an Independent Vegas can cause him to leave you if he catches you attacking any NCR. Since it is mandatory to go into the control room and activate Yes Man, this makes things a bit tricky. You don't have to worry about losing Boone if you have a mixed reputation with the NCR, like Wild Child and Soft-Hearted Devil. Another way to avoid losing Boone is to wear NCR armor, even though you're gaining infamy he won't leave because the disguise sets your NCR reputation to neutral.
If the player has destroyed the Securitron army below The Fort during the Legion quest Render Unto Caesar before deciding to fight for an independent Vegas, Yes Man will make several seemingly good natured passive-aggressive comments about this fact throughout "No Gods, No Masters", commenting on how "brave" the Courier was to go for the extra challenge of fighting both the NCR and the Legion without a standing army. These comments usually come with a thinly veiled frustration behind the happiness in his voice.
Behind the scenes
The phrase's origins date back to the French Revolution, a motto of which was "ni dieu, ni maître" -- "neither God, nor master." Since then, the phrase has been used by socialists (including anarchists and Marxists/communists) and feminists.
If you are listening to the NCR Emergency Radio during the final battle for Hoover Dam, among the chatter about positioning snipers and reinforcing positions you may hear lines, "They're coming out of the walls man! They're coming outta the damn walls!" and, "Game over man! GAME OVER!". This is a reference to Bill Paxton's character Private First Class William Hudson from the film Aliens.
PC After you receive the briefing from Yes Man about what needs to be done at Hoover Dam, the game presents a pop-up warning about moving into the endgame. If you do not say that you want to move on to the end of the game, and leave New Vegas, this quest will not load and the gate to enter New Vegas will be locked, preventing you from getting back into the Lucky 38.
PlayStation 3 If you choose to run back out of the gate before facing the Legate, then you can fast travel from the area. Doing so causes you to be unable to fast travel from another location. This can be dealt with by walking into a building and back out, but you must do this every time to continue fast traveling.
Xbox 360 After telling Yes Man that you're ready to go to the dam and if you have ED-E with you, ED-E will stay in the same spot where you start at, as no companions are allowed into the Lucky 38 penthouse, so he'll stay in wait mode as he was left as in the floor he was in. To fix this you have to open the companion wheel and tell ED-E to stay, afterwards tell ED-E to follow you.
Xbox 360 After the player has progressed in Render Unto Caesar to where you have to go to the dam, if you switch to Wild Card, when approaching Legate Lanius in his camp he will initiate the conversation from the beginning of Veni Vidi Vici. this will not activate the quest and you must make Lanius leave or kill him to finish the quest.