Acronis for disk image copy of the operating system disk, stored on multiple media, hard disk and a couple of copies on DVD.
All applications used are either on media or when installed/used are put into an apps folder and these are copied off also. My PC has office, Lightroom, and photoshop installed. A few other essentials and that's about it. I keep it quite clean.
In this way if I need to clean install then I can
Important file based backup every weekend to a nas and two separate USB disks. Basically this is email pst files, documents, all photo based files, raws, jpegs, Lightroom files etc.
I also have my course work on a blog, which is backed up every week and emailed to me.
Syncback is a free GUI based copy program which can be setup and only takes changes, as can robocopy as a command line. I run robocopy from a batch file as I find it's quicker.