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If you just pick up and start playing this game as any other point&click adventure game, you'll probably wind up with bad (or not so good) endings.

To get the best endings for the characters you need to be aware of the "Spiritual Barometer" - the background behind the character portrait. It starts out black, and then become lighter (black -> dark green-> ...->light green -> white) as you perform actions which raise your "spiritual health" and darker if you do the opposite. If you finish the character's story with their barometer "white", you'll get their best ending (as I understand it, I haven't finished the game yet). The Psych Profile is actually a hintbook, and looking at it will decrease your spiritual health, making it impossible to get to white.

Also save a lot, and whenever you hear an ominous sound and your character portrait makes an unhappy face - reload and try something else.

Alternatively just do what you like and see where that gets you, then if you wish replay the game and try for the best endings :)