The 3-2-1 backup rule is generally considered the best strategy. It means having three versions of files—two onsite and one offsite. That way, you'll be able to use the onsite backup copy to restore the primary version of your file quickly.
And should some unfortunate even compromise both onsite copies, you'll have the offsite one to fall back on. If you're unsure where to store your offsite copy, the online backup providers reviewed above are powerful, reliable, and easy to use.