I have a lot of problems with beating the Epicycles levels in Osmos -- do you have any tips for transitioning orbits without wasting a ton of material?
I think there are a couple key ideas that help for transitioning orbits. First, the path visualization is very useful to have on. On the orbiting levels, I tend to eject material only forward and reverse of my direction (except for emergency/panic maneuvers). I think that's the most efficient way to increase/reduce the size of one's orbit. Also, it's usually easier to increase the size of the orbit than reduce it.
The best way I've found is to break out of your current orbit in an arc that intersects where the next attractor will be.
When you get close, decelerate enough to prevent hitting the wall.
Stabilize your orbit.
Check this page out. It includes tips and a video playthrough of the hardest Epicycles level. http://www.hemispheregames.com/2010/02/03/osmos-rage-part-4-roadside-assistance/