Read them in publication order. Quite a lot of the novels will make references back to their preceding novels. Sometimes blatant and in your face, even returning characters etc. Others may just be little throwaway comments that you could almost miss, but are quite nice to pick up on.
You'll see and actually have already seen on this thread a bit of hate generated towards Battle for the Abyss, but bad as it is, read it anyway, it does at least have two interesting characters in it.
I would however suggest putting your face into a blender over reading Fear to Tread, it would certainly convey the horror of Signus better than the abortion that is Swallows attempt.