Eugene's observations

Below are the significant considerations in as compressed a format as possible.  One day your computer/tablet/phone (like almost all things) WILL fail and the degree of pain caused can be mitigated by acting right now.

Causes of failure.  Electrical disturbance, physical jolt, liquid ingress, virus attack, device driver corruption, Windows update failure, [inadvertently] downloaded rubbish, critical settings changed, fire, theft, flood, manufactured defect?

Destination Media.  Optical disk, USB thumb/pen drive, internal disk, portable or external drive, network attached storage, online cloud, another computer.  Which you choose depends on the degree of automation needed, size of data * frequency of copy * retention period, whether other devices are a factor.

Software.  Simple copy/paste would work but manual cataloguing required.  A program can automate the procedure whilst offering to encrypt the copy and compress it.  Some programs are free (e.g. Cobian, CrashPlan, File History) others come free with media or Internet security suites, but beware being trapped with one provider.  If the backup format is proprietary, make sure it can be recovered on another computer in a few years. Windows 7 comes with its own backup program and Windows 8 comes with File History.

Types of Backup.  Documents, photos and music are the minimum but also consider videos, e-mail (accounts and messages), browser favourite bookmarks, address books, configuration settings, activation keys, log files, device drivers.  Full backups copy all files, incremental backups copy files changed since the last backup, differential backups copy files changed since the last full backup.  An image backup is a bitwise copy of an entire partition that can be used to restore the whole caboodle ? some allow individual file recovery (e.g. Acronis) others not (e.g. Microsoft) most cost more than ?simple? backup programs.

Recovery.  Rehearse this every couple of months to ensure you remember how to when you have to and also to confirm that you really have backed up what you thought.  Some backup programs fail silently (e.g. File History) or you may have to look into a log file. 

Disaster Recovery.  Backups are a subset of a disaster recovery plan ? something that is essential if you depend on your computer.  Consider whether you can recover files to a different computer, do you carry a spare one, spare monitor/keyboard/mouse, is recovery software and media on hand. Are programs available to be reinstalled together with serial numbers for activation.  How time critical this is determines the cost.

RAID and Storage Spaces.  Redundancy can be enabled by using parity media to enable fault tolerance but in this case the entire volume must be backed up and a procedure established to alert when a failure occurs if automated fail-over is enabled.  Consider whether a duplicate RAID controller is required for recovery.  Do not hold images on volumes that are not available after a crash.

Synchronization.  Depending on the frequency and algorithm this could be a poor man?s backup but it is not intended as such.  Programs such as Syncback are free and can be reconfigured.