I always regard it as a challenge to play up the non-human nature of my PC's (& NPC's). And i try to reward players that do the same (My Shifter always growls when annoyed - sometimes its enough to quieten the entire party....)
Unfortunately, or fortunately, for a DM he can always rely on stereotype - you just need to establish the stereotype based on something alien and keep to it.
Now if your trying to create a truly alien race that you can then portray easily and simply you're always going to be struggling unless you can either find a cultural reference that your players relate to, or you have players that will work with you
Having said that - given the huge breadth of human culture, inuit to aborigine, new yorker to bangaldeshi farmer etc etc, why should non-human races have to be truly alien? Perhaps the most disturbing thing is that they're so similar to humans, but with only one truly alien traits......