How do I more efficiently reinstall Windows?

Well, doing a factory reinstall would give you a clue - there's a fair bit of background work. They essentially set up an unattended install script that'll install software on a fresh install, do initial setup and so on. You might also use post install scripts to run installations and setup user preferences.

For modern versions of windows, this would require the use of WAIK and building a reference installation. You might also have a script that installs software - there's a page on sourceforge that's an excellent resource on the switches for various installers.

However for us lesser mortals, who only do the rare installation...

Organisation is everything. I have a backed up folder with keys for a system. I have media (and download what I need directly off MS). I use rufus to build boot USBs (USB installs are faster)

I tend to do a fresh install, then get things updated with wsus offline update - I maintain a set of updates for the OSes I use directory so I don't need to download these each time.

Install software as far as possible in an automated fashion - I favour ninite but oneget or chocolaty is a better option. This ensures that I have the latest version, and is easier than wrangling everything manually.

In some cases I have folders with copies of my user settings. Hexchat for example has customization that date back decades and 3-4 different xchat forks for me, and I just copy these over.

I build it, make a 'gold' image, and use that when I need to reinstall by restoring that setup. Unlike a linux box, I do need to pull in software from multiple places at the moment, and this speeds things up, even when ninite covers most of my basics.

While I agree with the other answers, I think they somewhat miss the point. The question specifically asks about reinstalling Windows which is what I'll address here. I'm deliberately ignoring installing optional applications as they are not mentioned in the question and are already covered in the other answers.

There are a few ways to automate the installation of Windows so you don't have to "babysit" it.

1. Unattended answer file.

This is by far the easiest and simplest method. It is basically a text file (well, XML) that provides preset responses to all the questions asked during setup, so they are entered automatically.

https://technet.microsoft.com/en-us/library/cc785644(v=ws.10).aspx

(The above link provides the basics of how it works, there are various articles detailing specifics for Windows 7+)

2. Preinstalled images

Much like Norton Ghost used to do (and various other modern alternatives), all this is an image of a disk with Windows you have already installed on it that gets copied in whole when you want to "Install" a new machine. This is very similar to the "Factory restore" images that manufacturers supply with their machines - only when doing it privately, you have to manually install drivers afterwards if the "source" and "destination" machines differ sufficiently. For the most part, stock drivers and Windows Update are sufficient, especially if combined with a USB stick with a set of drivers for the big vendors - Intel, AMD, nVidia - most of them release unified driver packs these days that cover all recent products anyway.

3. Automated deployment

For larger-scale operations some companies use a centrally-driven auto-deployment system. In essence it's a combination of either 1. or 2. above and a central image repository and network booting infrastructure. This can cut down the entire install process to as little as start PC, press F12, press Y, but is quite a lot of effort to set up (though not entirely prohibitive for a superuser)

Of the above, most don't deal with the issue of installing Windows updates afterwards. As others have suggested, slipstreaming Windows update into your install disk itself is the most widely used method, but this means you do have to update your install disk/image regularly. Alternatively, switch to Windows 10, where Microsoft updates the images regularly, or use one of the slipstreamed "rollup" images you can often get via P2P (note, you can get "untouched" ones that do not have any pirated/cracked software on them, only genuine Microsoft updates, though even those are dubious in their legality)

In itself, none of them deal with licensing either, but most Windows installs will complete with an invalid or trial key or no key at all, allowing you or the user to enter a legitimate CD key and activate the product anytime up to several months after installing it.

Of course, if you're paid by the hour, having to babysit the machine all day might not be a bad thing.

Footnote: Technically, above-board "computer repair companies" can only legally reinstall Windows using the license and media that came with the machine - i.e. doing a factory restore - or using individual licenses. Installing your machine using my CD, but entering your license key, is legally ambiguous. Nobody would ever do anything about it, but I wouldn't do it on work time either.

As of Windows 8 and newer this is pretty much one click: How to refresh, reset, or restore your PC

If you want to do this manually i recommend:

• Have two partitions: one for the OS and apps (C:) and a second for data (D:). Try keeping data on D for example by setting the location of the Desktop, Documents, Downloads, etc folders on D. This way you speed up the backup before reinstall process by simply mostly have this already done/
• Get an Windows AiO ISO image : AiO means "all in one". These are images with have different possible editions and versions of one Windows system (32/64bit, home, pro, etc). They also usually have included recent Windows updates so you dont have a shorter update process. Example Windows 8.1 AiO
• Get WSUS Offline Update - this tool downloads windows updates offline and lets them install this updates offline. This saves you some time and a few manual restarts. Keep this on an USB flash drive. On older PC i usually let WSUS OU run overnight immidiately after a fresh install
• Have your tools ready - i have a USB flash drive with the most used programs i install over and over for example 7-zip, Firefox, Flash, CCCP Codec Pack, Power ISO, CD Burner XP, MS Office image, Adobe PDF reader/Foxit PDF Reader, TeamViewer QS, CCleaner, Malwarebytes Anti-Malware, Bitdefender Free. This way you dont have to search for them and download. You have them and installing them is a matter of 15 minutes. There are even programs where you can create a collection of this programs and the tool installs them for you automatically.

On a current PC (max 4 years old) such a reinstall i do in 1-2h with only 1h max being really 'active' at the computer.