Probably tons of different ways, but personally I use Macrium Reflect.
Nice feature is the ability to create UEFI bootable USB drive with Surface specific drivers and Bitlocker support, so that if Windows commits suicide you can boot from USB drive and restore from backup on external USB drive.
I'd suggest you get an external USB3 drive and a USB hub to enable USB boot drive and backup drive to be connected at the same time. Make sure you check it all works (including full restore) before you need to use it in anger. Also sometimes booting from USB3 devices can be problematic. I tend to use USB2 boot device but USB3 for backup drive. Alternative is to buy a big enough microSD card for the backup device, although I've had enough SD cards die on me to not trust this too much.
Any files that are really important then I'd also suggest using OneDrive / GoogleDrive / Dropbox so you know they are synced to the Cloud.
