The traditional reason for the lotus position and straight posture is to allign your Chakras so that your "third eye" chakra can be awakened.

The power of meditation comes from entering these deep states of brainwave activity. It takes monks years and years to be able to reach them normally (without any entheogens used). We have the advantage here because we can use THC to make our brain MUCH more sensitive to binaural beats. TurnyBright, I recommend getting Holosync's "Awakening" CD through any means. It'll help you reach those states of mind within the first few tries.