No one has "claimed" any of the Writer Guide updates for v3.5, so
please feel free to pick any chapter and go for it. You'll need to
look at the list of new features to see what might need to be done:
http://www.libreoffice.org/download/3-5-new-features-and-fixes/
IMO making screenshots look more consistent is way down the priority
list, in the "nice to have" category. Updating content and correcting
actual mistakes are at the top of the list, in the "essential"
category. I'm not saying "don't do low priority things", just asking
for people to do higher priority things if they feel comfortable doing
so.
You could spend an hour or two having a quick look through the PDF of
the compiled Writer Guide v3.4 that I created, checking it for errors.
I posted a note a day or so ago about what to look for in particular.
--Jean