There are 3 basic techniques:
1. Don't worry, be happy. This do-nothing technique seems to be most popular
2. File sync utility - examines the last modified time stamp of the files in your working folder and backup folder, and copy the ones that have changed
3. Image copy utility - completely copies everything on your working partition to your backup partition.
There's also the scheduling dimension. Some folks prefer automated backup on a defined schedule. Others prefer to do backups based on key events. Both approaches can work well. Deciding which is best for you depends more on your personality type than the technology.
I use SyncBack SE for file syncing and Acronis TrueImage for partition copies.