Premonitions are spontaneous, usually not something you can control.
As for OBE's, spiritually you are treading on some dangerous grounds.
Some have claimed to have reached this state at will through meditation, but I regard it as an opportunity for evil things to happen and evil entities having their way with you, just as you would by opening yourself to many occult practices. There is a reason the Bible warns us to stay away from these things. In fact, I felt that way about it even before I became a Christian from what I had read and understood of it. You could jack up more than just your brain.