Buy a good set of "hog ring" pliers, and a box of hog rings. You can get them at Tractor Supply.
The biggest tip I can offer is that when you put the covers on the backs, use heat to loosen the covers so that they stretch. A hot air gun (but don't hold it too close!) will loosen them up so that they'll stretch over the backs. If you don't get them on really tight, the material bunches up around the headrest and looks pretty bad.
I did mine, and they came out OK, but they are not perfect. But if I had to do it again, I'd pay a professional. If you can afford to have someone else do it, it would be money well spent.
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"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner