should I watch Mai otome 0 ~S.ifr~ first?

If you watched Mai Otome for once it's okay to watch Mai Otome 0~S.fr~ then. It has nothing to do with the Otome character's (except that there are some parents of the characters we already know (God, I remembered Shizuru's mother now ;__; )). But when you rewatch Otome, then watch Otome Zwei, too :3 (it isn't this good, but who cares -> Nao is awesome in there ;P). Anyway: Mai Otome 0~S.fr~ is the latest so it's okay to watch it in the end (even it plays before Otome)~
And have fun ^__^ (I should rewatch Otome, too >0<)
Edit:
Oh, you watched Mai Otome Zwei XDD Then just go watch 0~S.fr~ and then Otome again :3 Good idea, right?? ;P

^_^ What Kino-chan said. I started watching them all in release order (I had no choice at the time! Zwei and 0~S.fr~ weren't available yet! lol). Do the chronological order thing, the whole series will make better sense that way. Kinda like with Star Wars. Though...unlike Stars Wars, Mai Otome's prequel actually delivered. ;P So yeah, go in this order:

0~S.fr~
Mai Otome
Mai Otome Zwei

^_^ You'll be surprised how different Lena and Arika are....

You do get to see Miyu in the 2nd episode of 0 ~S.ifr~ if I remember correctly.

Not only in the 2nd epi. Miyu plays a more or less bigger role. But I think you don't see Alyssa-bird this much ;D

Even to this day, I'll never understand the Alyssa bird thing. XD It's cute, but random. The WTF type random.