Unplug and update drivers
Some of you may consider this step overly fastidious, but the first time Windows Update screws up a driver installation, you’ll thank me for this suggestion. Feel free to skip this section if you're using a prebuilt, boxed PC rather than a rig you've cobbled together yourself.
During a recent installation of Windows 8.1 on a test machine, I actually had Windows start installing a graphics driver in the background, while I already had a more recent version running. I spent the next half hour cleaning up the mess and starting over.
Take out the trash
First, run a tool like the amazing PC Decrapifier, which automates the process of cleaning out known bloatware. Then open the Control Panel, head to Programs > Programs and Features, and work your way through the list of currently installed programs, removing anything you’re not likely to use.
While you’re at it, fire up the Windows 8 Task Manager (Crtl + Shift + Esc), hit the Startup tab, and disable any background programs that don’t truly need to run when Windows launches. (If you're using a past version of Windows, search for "msconfig" in the Start menu and use the Startup tab there.) Often you’ll find dozens of programs that can be disabled, which will free up system memory and resources for other applications as well as speed up your boot time.
You’ll often find after installing an update or other Microsoft application (like Office, for example) that a number of new updates have become available. Continue to run Windows Update over and over and over again—restarting when necessary—until there are no more critical updates available for your PC. Once that's done, be sure to opt to have your computer automatically install Windows Updates as they become available, unless you have a compelling reason otherwise.
After your machine is fully updated, it’s time to install all of your favorite applications. I recommend taking this step after updating Windows itself to ensure all of the latest compatibility patches are installed, which is especially important with a fledgling OS like Windows 8.1. If you're wondering what to grab, check out PCWorld's guide to the 22 programs to install on your new PC first. It also talks about using a nifty tool/site called Ninite, which can automate the installation process of a number of popular applications, saving you a ton of time in the process.