To be honest, I think specific techniques, methods, or diet advice/deprivation are not necessary at all and may actually lead people astray. Many people cycle through different techniques and often get nowhere because the techniques are largely attempted shortcuts for getting to the correct state of being that induces an OBE.
In my opinion, the most important thing to emphasize is meditation done right. People are given a conception of meditation, typically from MBT here, and are left to their own devices in terms of how they practice it at varying levels of introspection and conscious effort. Even though meditation(for OBE) should be an act of letting go of sensory/mental input and typically by focusing on a singular point, I.E mantra, breath, or visualizing - there needs to be a consistent, concentrated effort on not just focusing on the meditation object but also in terms of recognizing when your mind is going astray or thoughts are popping up. At that point, awareness needs to be quickly and consistently re-directed to the meditation object(gently) over and over again with no frustration. The key is in this concentrated re-directing process because, after a while of exerting willpower over your mind through your intent, and not feeding it with any other input which would have your focus/awareness partitioned - your mind/body then begins to become subservient to the objective and begins to function completely inline with your intent or objective(to have awareness on one thing only). Simply in maintaining a very concentrated effort to re-direct focus on any input that springs up, I have found it surprisingly easy to go into altered states of consciousness.