Planning, planning, planning… and because it cannot be stressed enough, PLANNING.
11 minutes is a long animated piece… especially for a first-time animation. From the little you’ve described, it sounds like you may have chosen something a little overambitious (multiple scenes, multiple actors, etc.). Simplify as much as you possibly can. Is 11 minutes a requirement or have you already scripted and timed it out? If it isn’t try to say the same amout of stuff in less time and fewer characters and scenes. How detailed do your models have to be? Can they be simplified without sacrificing quality or whatever it is you’re communicating?
Storyboard. And put timing information with each board you draw. This is part of planning… so definitely make it a point to do this. It doesn’t matter if you can’t draw. Do stick-figure thumbnail drawings… but do enough that the idea, timing, and composition of the shot are all there… especially the timing.
Is there going to be any sound or dialog or music? Record that first. It will make the timing for your animation much easier.
Work in chunks… and do lots of tests (use the OpenGL preview rendering for this) to get your timing right.
Render in passes. If your background is static, only render a single frame of that and composite the animation over that in post.
Use matte painting where possible. If you can generate a background in Photoshop or Gimp, rather than model an entire scene, do that. It will save you time on renders.
Cheat or fake at every turn possible. If you have a character who’s just sitting still with no movement, just render them once and repeat the frame until they move again. If they’re sitting still, but reading, render the body once and just animate the eyes. Things like that will save you time in the end. Of course, pulling it off right requires - you guessed it - planning.
You’ve got a lot of work ahead of you. Don’t get discouraged and don’t get caught up in details that don’t add much to the finished piece.