There is a science devoted to transcendant experiences. Surat Shabd. A more western approach would be found in; Experiment in Depth
, by P.W. Martin. Here is a little.
Write your visions, dreams. Interpret. Dictionary of Symbols
by j.e. Cirlot.
Hone your abilities. Concentration; An Approach To Meditation
by Ernest Wood.
Keep a written journal.