Good lighting and good glasses (if you use them) are essential. Also, arranging yourself and warping board / heddles etc. so that you are not having to stretch or bend over to see the exact spot that you need to see. I also count and arrange heddles in small bunches as needed to complete small ‘chunks’ of threading, and then check straight away before knotting that bundle of warp threads together, for later sleying. Maybe you could colour code your heddle frames so it would be easier to distinguish one from the next when selecting heddles for threading.
Personally, I find the ‘lighting’ aspect problematic , as no matter how I place various lamps etc, there is always an issue with dark shadows in one direction or another. However, with such short days at this time of year, this is something I will just have to keep experimenting with. One last suggestion which may seem a bit daft…but I find that speaking/ counting out loud whether on warping board or when threading heddles in a particular order definitely helps. Hope some of that is useful!