As promised (threatened?), here is how I backup my data. All my desktop's data backups (with one exception I will cover in a moment) are kept on internal type HDDs that are stored externally in a drawer. I have a 3.5" dock built into my computer I can plug the backup HDDs into when updating a backup. You could use a dock permanently connected to your computer (USB 3.0 or e-SATA are the fastest connection) and only put a backup HDD into the dock when updating the backup or you could use commercial external HDDs (the latter would be a bit more cumbersome to use plus the drive quality is usually lower).
I'm a bit anal (ok, really OCD anal) when it comes to backups so I have four backup HDDs for every HDD installed in my desktop computer. I keep two of each set of four stored in a drawer at home and the other two of the four in my safe deposit box at my friendly, neighborhood credit union. I swap the HDDs in my safe deposit box with the ones at home no less than once a month; more often if I've been adding a lot of data.
Why so many backups? Well, when boiled down to the lowest common denominator, there are only two kinds of HDDs: those that have already failed and those that haven't failed yet. Any HDD can fail at any time without warning, even the best ones. I received a 4TB WD Black, one of the best drives made, that was DOA late last year. Since even backup HDDs can fail, the more identical backups one has (up to the point it becomes too cumbersome and expensive, of course), the less chance of one losing data due to a failed backup HDD. I did have a situation where my main data drive mysteriously became corrupted (ok, it was user error

) and I managed to lose it and one of my backup HDDs. Fortunately, I still had the data on the second local backup HDD and, after reformatting the two corrupted HDDs, I was able to fairly quickly recover the data back to the computer's HDD and the other backup HDD. Still, most people can get by with one onsite backup and one offsite backup, depending on how valuable their data is to them and how tight their budget is or isn't. An acceptable bare bones setup would be one local backup HDD and either a Carbonite account for the offsite backup and/or a second backup HDD stored off site somewhere.
Since the same kind of disaster that can cause data on a HDD inside a computer to be lost can also cause an externally stored backup HDD to lose data, such as fire, flood, theft, etc. By having backup HDDs in a secure offsite location (such as my safe deposit box; a friend's house, etc. would also work well), if the unthinkable should ever happen and you lose all your data at home, you will still have the offsite data to fall back on.
Here's that exception I mentioned. Since an offsite backup won't have any data that was added or changed after the last time the backup was updated, I also use
Carbonite.com, a cloud backup service, to fill in that gap. A basic plan costs only $60/year. I have it set to update only once a day so it won't waste bandwidth backing up scratch files I may use only for a short while, then discard, saving internet bandwidth usage. However, it can be set to continuously backup 24/7 or, if you put an important file on the computer, be manually told to back it up immediately. Carbonite can be used by itself for an offsite backup but, if one has a lot of data, recovering data from Carbonite can take days, weeks, or even months, depending on the amount of data and the speed of the internet connection. Also, since even a cloud backup service can fail, it's not a good idea to totally depend on one for backups. If I should lose all my data at home, I can recover most of my data from my offsite backups and get the rest that was added or changed since I last updated the offsite backups from Carbonite, dramatically reducing the amount of time needed to recover all of my data.
While imaging is the most efficient and effective way to backup one's system files, it is grossly inefficient for backing up data. First, it takes too long because you have to image all of your data every time you update your backup and second, it requires a lot of space to store the images. Some people use incremental imaging to avoid that problem but, as mentioned before, incremental imaging is not without its problems and would be better eschewed.
Folder/file syncing programs, when set to Mirror mode, compare the contents of the folders you designate on the drive to be backed up (you can designate an entire drive, treating it like a folder) with the ones on the backup drive, looking for any changes between the two. The program will then copy and paste from the source drive to the destination drive and delete files from the destination drive as necessary to make the destination drive essentially a clone of the source drive. Since only new, changed, and deleted files are processed, backups can be considerably faster than imaging, which has to process every file every time, and requires less room to store. Rarely, if ever, does a backup drive need to be larger than the source drive.
FreeFileSync is my
weapon folder/file syncing program of choice but I'm not going to go into how to use it right now. One of our members here has a
nice little video showing how to use it and, one of these days, I'm going to write a more detailed tutorial on how to use it for backups, including versioning, that one can print out (something I prefer over videos since, at my age, the only thing I retain well is water and fat). Right now, I have too much on my plate and my old carcass just isn't cooperating.