I am kinda new to anime. I started watching it back at the start of the year.
So what are those anime about?
Mai Otome 0 ~S.ifr is the prequel OVA of Mai Otome (which in turn, is an alternate universe, Mai HiME spin off). Great, but not recommended if you haven't seen either HiME or Otome (just watch HiME, and ignore the Otome universe).
Slayers Revolution is the 4th Slayers series, and direct sequel of all of those... so, if you aren't a follower of Lina Inverse's adventures, then I wouldn't recommend it. Still, watch the original Slayers if you can, it's a pretty fun and interesting anime (Slayers Next is as well).
I'm ignoring both Slayers Revolution (didn't watch the previous seasons, only the first so I doubt I could follow it) and the Mai Otome OVAs (dunno why but I don't like the Otome setting much and the OVA parts I've seen weren't interesting IMO).
well, I don't blame you, Mai Otome & Zwei mostly sucked... yet 0 ~S.ifr in it's 2 released episodes (the final one will be available in November I think) is far far better already...