Not knowing exactly where you are helps. You can achieve this by spinning, zooming upwards out of the atmosphere, or momentarily filling your visual field with a patterned surface and nothing else. Exiting your room via a portal (such as a window or mirror) also helps, as does trying to enter a picture. Just staying out for a long time tends to gravitate you towards the astral as well.
Very carefully, hopefully.
You need a quantum rocket capable or traversing non-euclidean dimensions.
You need at least a level 9 cleric or druid.
By eating cheese before bedtime.