1) Bad Endings
	1a) If you wander around one of the other buildings for no reason when there are patrolmen around, you'll get caught, and your life will suck. Duh. (also, there's a special version of this on day 16)
	1b) If you make enough bad choices in the ELPOD (bad = dishonest with your main character's self), then on day 12, during the MINMES scene, your mind will collapse. It's actually very cute; try it.
	1c) If you make good choices for the first six ELPOD scenes to avoid the bad ending above. Then choose horrendously on the seventh and eighth scenes (on days 12 and 13) and you'll mentally collapse during the day 14 school life fantasy scene. This one's also pretty cute, and it's worth hearing Youko give you the hint afterwards.
	1d) The final boss battle is essentially a looping decision tree with only one way out. If you made certain bad choices in recent ELPOD scenes, you may see a bad ending here.

2) Normal/True Ending
As with many visual novels, there is the ending you are most likely to get, as well as a special one if you make just the right choices at some point in the game.  Since figuring this out on your own is part of the fun of a VN, I'll list various levels of hints before telling you exactly what to do.  But keep in mind: when I say "choice," I don't necessarily mean choices the game spells out for you.  Sometimes things can change based on where you go during a map segment.

	Hint 0: In case you didn't notice, when you finish the game with the normal ending you will be given the opportunity to listen to the game's hint regarding whichever choice you did not get right.

	Hint 1: There's one vital choice for Yui and one for Haruka.  Nothing else in the game matters in determining your ending.

	Hint 2: Each vital choice takes place when the facility is on alert and the background is red.

	Hint 3: With both choices, the goal is to bring the "Lost Body" in contact with another major character who can help them.

	Hint 4: Both choices require you to go to the right place during a map segment.

	Hint 5: Both choices require you to enter, or at least try to enter, a specific room.

	Hint 6: Yui's choice requires you to try finding Yui during the day 6 emergency, while Haruka's choice requires you to try finding the nameless boy during the day 12 emergency.

	Yui's Answer: When you enter Building C during the day 6 emergency, move down two and left two so that you're at a three-way intersection. Now move up three (shaking off the patrolman), then left two.  Below you is the Building C Relaxation Room where Yui is hiding.  Find her, talk to her, then tell her to go back to Building B so that she will leave this room and meet Yuri in the next scene.
	Making this choice changes most of the events of day 7. Even if you got this right the first time, you may want to go back to see the other version of events.

	Haruka's Answer: When you are mysteriously dropped into the day 14 emergency, start running, since you have no other choice. Go left, then around the four-room cluster at the Building's core, then back to your room.  Attempt to enter your room. You will fail to do so before Haruka catches up to you, but this will allow the nameless boy to save her life, as revealed in the next scene.
	Making this choice changes the day 13 opening, and not much else. If you got this right the first time you likely didn't notice.

	Making both of these choices will add an extra scene to day 20 and the game's ending.  Naturally, these new scenes have Yui and Haruka in them.

3) CG collection
	First, watch the first three bad endings to get their CGs.
	Second, replay ELPOD scenes 7 and 8 (on days 12 and 13) and make all possible bad choices if you didn't already.  In a similar vein, go back to the conversation you had with Haruka on day 2 and retry those choices.
	Third, and most absurd: on day seven, at night, examine the rear wall of Youko's room (just below yours). You may have examined this spot before and noticed there's a ventilation duct. By examining it at this exact time, you get a CG. You can probably guess what it's of. (this seems to only happen if you made two past choices correctly, though I can't decipher the code well enough to figure out which ones).

This advice is partially based on the Japanese walkthrough at: 
http://www008.upp.so-net.ne.jp/SNOW/