To start with, I am not experienced in any way in the art of salvaging things (in general, in specific I have been able to fix a few things that other people either have or would have thrown away) in the traditional sense of dumpster diving or rooting through abandoned buildings for whatever may be available (as rooting through occupied buildings amounts to stealing). So on that note, I’ve been thinking about the various steps that one would take when looking at salvage in a post apocalyptic setting.
One consideration that you would have would be the various dangers one has in leaving whatever safe location you are already at, be they be zombie hordes, lingering radiation, robots, or even other survivors. Tactics and methods of dealing with those issues are not what I’m trying to focus on here, but I can imagine that they would likely impact your salvaging operations nonetheless. This might impact the time (or time of day) you can spend away from your home base, whether or not you can even establish a home base (as you have to stay on the move to avoid ever expanding grey goo), or what tools you can bring with you to help with you salvaging (such as enhancing carrying devices like cars or grocery carts, or the safety of bringing weapons).
Another consideration is the number of people (or other resources) that you have that could help you in the process of salvaging. If you’re by yourself, many of the following tasks might be linked together than if you have a group, or if you have access to drones or other remotely controlled devices. Once you are dealing with more than just yourself, skills and preferences for different tasks should be considered as well as considering rotation of duties to keep people fresh and aware of the tasks your fellow group members are engaged in (the counter consideration is that specialization may not be as easy with rotation).
Having a method of communicating or marking each site as having reached a certain step in the order of salvaging saves your own team from walking in circles, and communicates what each site needs next.
First in the order of salvaging operations would be reconnaissance; you need to find where there is stuff to be able to salvage. Maps are a great help here, as well as having advice from a local (who actually knows the area, not just one who ‘lives there but hardly ever visits the neighborhood’). Being able to get to a higher elevation can give you an idea of which buildings appear to be more intact than others and thus likely to have more of whatever you’re looking for, and having a telescope, binoculars, or even a camera with a zoom lens is valuable here. If you’re able to spare resources to go out and do just reconnaissance, they can save later groups a lot of time.
Second is to grab the stuff that is most valuable or vital at that moment. This can change from time to time as your resources (hopefully) wax and (hopefully not) wane. It also depends on what or who you are … if you’re a robot, than food may have little use to you, but replacement parts or batteries might be. This step could be combined with reconnaissance, but it may not be possible for the resources you use for reconnaissance (such as flying drones) to be able to pick up materials, and it may also slow down those who can pick that stuff up; if you have people to spare, splitting tasks would be useful.
Third is to do a more thorough search of a site than just the quick grab that the second step covered based on the first step’s observation. This doesn’t necessarily mean a full inventory, recording what is where in every single site that you visit, but if you have the time, knowing where a particular hardly ever used item is would be useful when that item is in need. This is the bulk of what I believe most people consider salvaging.
Fourth is a somewhat counter intuitive step, but it is the securing of a site. If the site still has materials in it that can be used, but you either do not have need of it now or do not have the means to salvage it now (it’s too big, you’ve run out of storage space, it’s too difficult to break down to transport), having that site still viable in the future is important. If water is still running, it should be drained out of the pipes and the water shut off (as should the gas, noting that if you don’t have ready access to water, saving this water someway would be better than letting it freeze in the pipes … you’d lose the building and the water that way). Power should be shut off as well. Windows and doors should be closed (even interior doors) and sealed as best as possible. The intrusion of water, plants, or animals can lead to a building falling apart faster than it being left on its own. With ideal resources, windows should be boarded up to protect from birds or hail breaking them.
This fourth step (or group) may be necessary earlier than the third step, depending on circumstances; a thorough search of a house may not be possible if the neighborhood is about to burn down … you either abandon it or fight the fire. Also some of the faster steps (such as shutting off the water, gas, and power) may be done by either the first or second groups, depending on the risk (winter is coming, gas explosions are destroying buildings).
The final step is only possible with the proper resources; the whole scale salvaging of a site. This isn’t merely walking off with what isn’t nailed down, it’s bringing a claw hammer and getting everything else. Doors, windows, insulation, pipes, wires, floorboards, the kitchen sink, these are all manufactured goods that may not be readily available post apocalypse, and can be repurposed for other tasks (garage doors make for decent walls). Many of these things may not be suitable for easy disassembly, but burning wood salvaged from a house might be easier than finding a forest and cutting down a tree, depending on where you are.