Night 1-4 strategy:
I can't guarantee it's the correct one but it worked for me. The breathing can have a little variance and is sometimes preceded by mechanical noise, so listen out for that.

Night 1: No Foxy
Check both doors, wait for ~5 seconds before shining flashlight, if you hear breathing, close the door and keep it shut for ~5 seconds instead.
Check the bed and hold the flashlight every so often until the Freddles disperse.

Night 2: Chance of Foxy
as above
If the closet door moves, head there. I'm not sure whether you need to flash first or not (I always did), then you need to keep the door closed.

The longer it's closed the more chance Foxy will revert to a plushie (flash to check), but I'm sure it happens in stages and any amount of time decreases the time that Foxy will kill you. Once Foxy is a plushie or if you're worried about the doors go back, you'll need to repeat this process of closing the door on Foxy from now on.

Night 3: High chance of Foxy
as above

Night 4: Very high chance of Foxy
as above

Nights 1-5:

Night 5: Fredbear only
Sound cues are the only thing that matters on this night so you need to listen hard. You get plenty of time to react but only briefly flash him if he's in the halls else he kills you (it may be better not to flash at all- haven't tried that but reportedly others did).

There are roughly 3 sound cues, two of footsteps going left or right and his laughter. The one that reveals his position is the last one that started, and he can move through the room.

So e.g. if you hear footsteps then immediately after laughter, he's in the room.

If you hear laughter and then immediately after footsteps, it doesn't matter that the laughter can last a lot longer, he's in the hall.

If he's in the hall, close the doors and keep them shut until he moves or laughs. Bear in mind if you flash, you might not see Fredbear unless you flash several times, this is because he's trying to trick you into thinking he isn't there. Trust your ears, if you heard him and he hasn't moved or laughed, that's where he is, trick or not.

If he laughs and is in the room, check the bed and hold or spam the light at him, if he's in the closet, keep the doors shut. Both time's be ready for him to walk instantly, I find this is the hardest part, since all other times he alternates, but at this point, he could go either way, listen carefully while doing this because if you pick the wrong side, you'll lose.

Night 6:

This is a harder version of Night 4 and Night 5 combined. At around 4am, Fredbear will replace the other animatronics (including Foxy and the Freddles if there are any).

If the Freddles suddenly stop appearing on the bed, you've got Fredbear. Use this as your cue to change your method, since following the Night 4 method will get you killed if Fredbear is hiding in the halls.

Night 6 onwards:

Night 7:

Same as night 6 except with a new animatronic that works a lot like Fredbear, except that he is a lot faster, alternates very quickly left and right, and doesn't seem to play tricks like hiding in the halls.

Night 8 exists in FNAF4.

It's a more difficult version of Nightmare(Night 7), with a high chance of Foxy appearing before Nightmare does.

I'm not going to write in the guide how to get it (yet), with experimentation anyone can get it.
edit: okay the solution is given in several YouTube videos now, so here's how:
Type 20202020 (top keys not NUMPAD) while in the Extras menu and it'll turn from Nightmare to 20/20/20/20.

When you complete it you will gain a 4th star. You don't see The Chest again.

My Night 8 Completion

First ever Night 8 Completion (DinkyDana)

No idea how to get these or if they even exist. Feel free to leave a comment or come to the stream and let me know if you know how to get either or both.

Pretty simple, just keep the flashlight switched off and listen for his movements, he should move around 3 times, the 3rd time he is creeping up on you, you need to flash him then when he's on the X.

On every subsequent night you get less time to stop him on the X, flashing him will slow him down esp. if timed badly, so you need to not flash him too much to get him on the X in time.

Succeeding will start you at 2am instead of 12am for the next night only (if you fail that night, you'll be on it at 12am again).

In the minigame (night 2?) where you are outside the pizzaria and it's telling you have just enough time to run, you go right and you get blocked by Fredbear. Then go left. Immediately turn and go back right when you get to the next screen for an Easter Egg. I missed this one myself but people in chat told me about it.



Sometimes when you look back at the bed (usually middle of the night for me), there will be an IV Drip Stand by the side of the bed, it will stay there for a few seconds then disappear again.

A few things this might mean:

1. This is happening after the bite, but we don't always see the stand because the kid is already hallucinating.

2. The IV Drip Stand is a vision from the future.

3. The kid might be sick and use an IV Drip normally, so he hallucinates about it.

Technical stuff & FAQ:

How to stream FNAF4 in OBS?
Game Capture won't work, use Window Capture. (was asked in my stream)

How to reset the desktop resolution after FNAF4 starts?
When I started FNAF4 it reset my desktop resolution to 1024, to get it back, just use your normal method for setting it. E.g. for me it was right click on the desktop and select Screen Resolution and set it back to 1920.

Other FAQ can go here.

If you want to be added to credits or contributors, send in an image or easter egg, and feel free to mention in the comments.

If you found the guide helped to pass a night (main function of the guide) please rate and thanks for reading.

Credits:
Ricky447LP, first person on my friendslist to find this guide and favourite it at just 5 unique visitors (including me). That means he's really fast, faster than Sanic. Thanks Ricky :)

Samarai(Twitch name). The guy who was on my stream who along with Ricky convinced me that footsteps were a thing on Night 5 even though I thought otherwise, and so thanks to both of them I passed Night 5.