I'm focusing a bit on brushes next year, myself. Here's what I've done...
I took an inventory of my current brush collection and wrote down what I like or dislike about each, plus how I use it. Then I noted if I want to keep it, whether or not I want to back it up (if I really like it), and/or if I want to replace it or find another use for it.
From there I did the online version of window shopping: I looked around various websites -- mainly ones of brands (or that sell brands) I use and like already, as well as brands I want to try out -- to find shapes I want, be it shapes that I don't have to fill gaps, or even shapes I do have but may want in another size. Or shapes and densities that I think may serve a particular need or want better than what I already own.
Also: I watched brush reviews on Youtube, centred on those brands that I want to look into (in my case, Hakuhodo, Chikuhodo, and Rae Morris). The more in-depth, the better, IMO. Since my only buying option is online, this sort of thing is an immense help. In-depth, written brush reviews on blogs have also been useful to me. (Also useful: the Brush Temple at sweetmakeuptemptations.com; Sonia's got a massive collection of makeup brushes with reviews and comparisons.)