I recommend trying to move in a way that would be impossible in waking life, rather than rolling out of bed in the way you normally would with your physical body. That way you can avoid the risk of rolling out for real and ending up falling painfully on the floor! Once you've transitioned into the dreamstate, you can move in all kinds of ways that would not be possible for your physical body, so these actions can also act as a reliable RC, in addition to being a heck a lot safer.

There are plenty of options:
  • rotate laterally (spinning sideways like a helicopter blade)
  • rotate vertically (spinning vertically like a windmill blade)
  • slide horizontally in any direction (without moving your limbs)
  • sink down into the bed
  • float up toward the ceiling

If you can manage any of these, it will serve as positive proof that you're dreaming, and moreover avoid not only the physical danger of actually falling off the bed, but also the nuisance of accidentally moving your real muscles and disrupting your passage into the dreamstate.