In my case- I started making top 30 lists in 2013 (which became top 50 in 2014 onward because of the sheer amount of music I was consuming due to streaming and What.CD)-- sometimes accompanied by long blog posts, sometimes just a playlist. At some point, I went back and made lists for 2010-2012. I tend to have a list of roughly 50 albums that I've liked come December and then the end of the year lists hit and I use AlbumoftheYear.org to sift through what I may have missed. I also tend to update past years on occasion just via my personal files.
So when I started my top 200 of the decade- it was as simple as going through those old lists + beginning to re-listen to stuff that I used to love but maybe never purchased on vinyl + re-approaching stuff that I had never really given a chance either due to the timing of the release (ala D' Angelo) or the fact that my taste has shifted over the course of the decade due to key releases that opened my ears to new genres.
I've always had eclectic taste (in any medium I tend to value that which is playing with form and challenging boundaries), but my bread and butter entering the decade was definitely alt-rock/metal, classic rock, indie rock, downtempo electronica and (underground leaning) hip-hop. I look at my list now and am blown away by all the R&B, pop, punk and auto-tune tinged (which I used to despise) music within my list. And also just how deeply in love I've fallen with non-EDM electronic music.
In fact I think the hardest part in making this sort of list was prioritizing albums that literally changed my taste in music (Art Angels/Visions, Summertime 06', Freetown Sound, Malibu, Saturation II) versus personal favorites that were already up my alley (American Dream, Sometimes I Sit, Blackstar, To Pimp a Butterfly, Painted Shut, Teens of Denial). I tended to prioritize the former.
Also, I think what's special to me about this decade is the way in which a) major labels lost control of the creative process b) that resulted in the crumbling of genre as we know it.