Post #1, you are in the position of currently having an older OS (windows 7 or 8.1), you have just downloaded windows 10's installer files but have't begun installation yet?
If that's the case you need to make a system image on an external drive before you do anything, this can be done using the tools under "windows 7 file recovery" or "file history" (depending on which OS you have right now). Such an image will let you rstore your system from a damaged state to it's current state if something goes wrong during upgrade or at a later time. It'll also make it much easier to get back to your current system state if you find you don't like windows 10 and want to go back. Other useful things to make would be a system image using a non-microsoft tool (macrium has a free image making tool) as an alternative should something go wrong with the image made by windows' internal tool. You should also make some recovery discs/USBs, these aren't much use alone but they'll help you get to the recovery environment, at which point you can use a system image, if something goes so badly wrong you can't even boot.
When it comes to making the image with windows' internal tool go to "windows 7 file recovery" or "file history", then "system mage backup" or "make a system image" (again what it is called varies depending on your current OS), then follow through this tutorial. http://www.bleepingcomputer.com/tutorials/create-system-image-in-windows-7-8/#manual
As a general rule making such images should be the very first thing you do on a new computer, and you should always make sure to have good (as in, made at a time when your system was running as you liked it, all the programs you like installed, all the junkware removed, no viruses present...) system images saved on external drives somewhere incase of disaster, they can be helpful in fixng many other computer problems alongside their use in restoring yourself to a working state if you hit problems during an upgrade of any kind.
P.S. regarding your pesonal files, I wouldn't trust file history alone to nackup your personal files in circumstances like this, make sure to manually copy them to an external drive, USb, DVD, cd or upload them to a cloud storage service (not a synced one, syncing carries to many potential ways that a synced file could be modfied and damaged).
britechguy, I quite agree with you on that mention of "During periods where my system is stable in the sense of I haven't been installing or tweaking things much or at all since the last system image backup I can go for months without doing one" you don't need to make system images regularly, you just have to make sure to have some really old ones about from when the system was nearly brand new and have some from just after the last big change you made to your system which would be bothersome to repeat, system image making isn't a task you do every X months, it's a task you do a few times when you know your system is in perfect condition. Backing up personal files to USB/dvd/cd/external HDD/cloud storage though, this should be done daily, anything you've modified that day you backup in the evening.
Edited by rp88, 11 November 2015 - 12:39 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB