generally speaking, avoid cartoony eyes and human shoulder/torso anatomy.
if we get pedantic, though, it's better to focus on what you like and don't like rather than trying to avoid the relative vagueness of 'the furries', they're a diverse group. no matter what you do, there's going to be a furry out there doing the same thing. so the decision between 'hands' and 'paws' is unlikely to be very easy if it's based on trying to read your future player's mind and know which of the two options they happen to consider to be "more furry".
on the technical side, figuring out what animals you even want to use is also a good place to start. even with scratch-built animal people, taking a look at the anatomy and behavior of various animals that have similar traits will help you actually build the things. chances are, what you or anyone defines as 'furry' are more stylistic qualities in the art rather than the actual composition of the characters themselves. ymmv, but sometimes stylistic decisions like that can be made harder than necessary if you don't actually have a basic 'prototype' or 'blueprint' of your character(s) already in your head/on paper/wherever.