(Actually, to San Francisco, then Navarro, back to San Francisco)
The first San Francisco/Navarro block consists of getting the Advanced Power Armor. The armor will make the game significantly easier. You don't have to get it immediately, but be sure to get it after finishing the Vault City / Gecko block (see later sections).
Head south of Arroyo, way down. If you start to see the coast, go east and then head south until you reach San Francisco. The city is located right next to the coast. If you find some really hard critters on your way there, be sure to run away. It might take about four weeks to walk there. San Francisco is marked as "unknown" on the world map.
Once in San Francisco, go north up the street, and take a left after you see the boxing ring. Go south and enter the Brotherhood of Steel building. (It has a guard in metal armor standing next to it.) Talk to the guard, ask why he knows your name, and then ask who the Brotherhood of Steel is. He'll start talking about the history of the Brotherhood of Steel and then mention the Enclave. Offer to infiltrate one of the Enclave's bases at Navarro, and then ask him how to go about infiltrating the base. The guard will tell you. Head to Navarro for now.
After you get in Navarro, talk to Chris, the gas station attendant. Tell him that you are looking to join the Enclave, and then tell him that you are a new recruit. Chris will give you the password. Head north to go to the Enclave installation.
Once you are there, talk to the guard, and give him the password, which is Sheepshead. Enter the Enclave, and go to one of the buildings to the north that has some people in lab coats. Talk to one of those people, and ask him if he knows where the Vertibird plans are kept.
After you get the info, go to the eastern maintenance building and talk to Quincy, one of the men in leather armor. Ask him if you can see the Vertibird plans. He'll ask you who needed them, and then tell him that Raul needed them. He'll get really angry, but will let you take the plans. While you're at it, be sure to loot the other lockers for a lot more stuff.
After you get the plans, go to the western maintenance building and talk to Raul, the Vertibird repairman. Tell him that Quincy wants to see him. Raul will get really angry at Quincy, and then he'll ask you to look after the Vertibirds. Offer to do so, and when Raul leaves, loot the lockers to get more stuff. After you've looted them, go to the basement of the base. There is an elevator in the northern section of the base.
Once you're in the basement, go south and left, and loot the lockers there. Get an Advanced Power Armor, but not necessarily the weapons and ammo. Leave the base, and head back to San Francisco.
When you're in San Francisco, go give the Vertibird plans to the Brotherhood guard. He'll make copies and give you back the plans, and also will give you full access to the Brotherhood facilities. You don't have to, but if you want, take the Power Armor and the Combat Armor from the base. Leave for Klamath. The walkthrough will be covered as if you didn't get the Power Armor, but there will be specific things that you can do with the armor, and those will also be included.