So the aim of the game here is to get into your neighbour's house, and find his secrets. And, oh, there are secrets. He's hiding away a few fantastical things in the depths of his abode, and it's up to you to seek them out. Getting in there won't be easy though, as the neighbour is watching. If he sees you, he'll throw things at you and seek you down. Luckily you can walk slowly and use the walls and corners of the house to hide and make progress unaware.
Operation distraction
So how do we get in without him noticing? Well, the easiest way is to cause a distraction. On the left side of his house you'll be able to find an electrical switch. You know where this is going. Flipping the switch will trip the electrics in the house, causing the neighbour to start looking at what's going on. This will cause him to open one of the doors in his house, allowing you to make entry, if you can do it undercover.
Perfect stealth?
Of course, the best way to make it through is with perfect stealth, in every sense of the word. It's possible, just difficult. You'll need to stay behind the neighbour, if you ever need to pass him by, and tiptoe your way around the dungeon-like building to make sure you don't get caught. But also, in your early tries, don't be too afraid to just run in, find a method of progression, and then using what you've learnt on your next time through. It is basically a roguelike, after all. You can use his cupboards and wardrobes to hide away in if he's onto you, but they're not perfect...
Windows? More like win-NOs
If you can't find an entrance, or a distraction, make your own, right? Exactly. If you need to make a quick escape - or a daring entrance - you can take out a window and jump straight through. Hold the item button when looking at small items, and you'll be able to pick them up. A second tap will throw them, smashing any windows in the way. You'll also notice the neighbour himself like to just, erm, stroll through windows sometimes. It's quicker, I suppose?
Nosy neighbours...