1. Some of the bathrooms in Japan are "unit baths" which include a shower, bathtub and toilet in the same room. Older style bathrooms may be separated into a "water closet" (a small room with just a toilet) and another room with a shower and a Japanese bath (usually a deep, square tub). If you have a water closet, or any narrow closet-like space which has no or insufficient built-in shelving, you can buy a tension bar shelf to give you a place to store medium to light-weight items such as facial tissues, extra toilet paper, and hygiene products. If you get it good and tight, you may even be able to store heavier items. I have a gallon-size container of "Simple Green" cleaning fluid on mine and the bar hasn't fallen.
2. Use the top of your refrigerator wisely and purposefully. First of all, don't make the top of your fridge extra long-term storage space for that crock pot you use once a month or so. Nothing is worse than seeing a bunch of appliances or junk on top of a refrigerator. Things get dusty and look a mess. It just screams, "I don't have enough space and I'm shoving stuff there". If you want to use that space, use it for ready access to things you use all the time and organize it well. That means leave some open space there so you can slide things in and out without difficulty or knocking things down or off. Nothing should be on top of your fridge that doesn't get used or consumed on a regular basis.
I realize this is an accident waiting to happen in a big earthquake but I figure I'll have bigger issues if there's one big enough to topple my coffee makers.
3. Use free-standing shelves to elevate items on large, clear surfaces to double your capacity without using up more counter space (see picture above). Use metal shelves for relatively heavier items, plastic will suffice for lighter items. If you've got one of those little dorm-size refrigerators that foreigners often start off with in Japanese apartments, you're a good candidate for interlocking stacking shelves (like the metal one on my fridge above). You can stack them up and create levels of shelving if you like, putting commonly-used kitchen items on them. To provide stability, put heavier items on the lowest shelf. It's also better not to stack higher than two shelves if you use the cheap, plastic ones that you can get at hundred yen shops.
3. Decant food from its original packaging into containers to present a unified look for your food storage and store more efficiently. Using the same style containers actually makes a space seem longer because it provides a uniform look across the available space. The eye is drawn along the space rather than overwhelmed by clutter. Also, there's nothing uglier and more unwieldy than a collection of various bags and containers. They are much harder to store because of their varying sizes and shapes. You tend to find yourself struggling to dig bags of flour or bread crumbs from a jumbled pile in limited storage space. Decant everything which comes in a paper or plastic sack (coffee, sugar, etc.) or that comes in a large box (teabags) into containers (tall is better) . Store any excess that won't fit into your container out of sight in its original bag and put your containers in a place close to your food preparation area.
Computer accessories and cables that I use on occasion and printer supplies are in baskets in the narrow space under my desk. They're where I need them without being in the way or taking up valuable shelf space or desk space.
4. Use baskets to organize convenient storage in small and/or narrow areas. Generally, I think baskets are a bad idea but that's only if they're used to organize large spaces. For narrow spaces, they can function essentially as drawers. You slide them out and get what you need and slide them back in. If you pick the right size, you can push them back just far enough that they are out of view except at extreme angles but are still in easy grasping range.
5. Use clip lights instead of lamps for dark areas, especially for reading or detailed work. Lamps are good for decor but, in very small places, it's often the case that surface areas are at a premium. You can get a lot of attractive or unobtrusive clip lights from places like Amazon and they cost no more than a conventional light.
6. Use rolling furniture in necessary large dead spaces. As a previous tip, I mentioned using dead space for storage. This works well for small, narrow, or out of the way dead space but sometimes you are forced to accept large dead spaces. In my case, the cabinets under my stove need clearance to open so I can't put a permanent piece of furniture in front of them but I desperately need more storage in my kitchen. To get around this, I bought a rolling shelf that I leave in place most of the time and only roll out to take items out of the cabinet (I organize my cabinet so items stored in there are accessed relatively infrequently). It provides a great deal of storage space both for long-term items and for things I need to access immediately.
7. Hang up kitchen items if you can but only if it is relatively unobtrusive and opaque. You often see modern kitchens with an island in the center and a huge collection of pans hanging over them. This might work in a bigger place but hanging stuff out in the middle isn't so great when you're in a tiny place. In fact, I'd strongly recommend avoiding hanging things if it creates too great a bulge or visual focal point. That doesn't mean you can't find some reasonably good nooks and crannies to hang things in which will help with your storage issues. I hang umbrellas by the door in front of the washing machine, and a frying pan on a shelf by the stove. You can also hang more dishes in your cupboards using hooks inside if your shelves aren't custom sized for dishes.
8. To make a small space feel bigger and like you have room to breath, try to keep much of your flat surface areas clear. Give the items you place on surfaces breathing room around them so the atmosphere isn't "cramped" feeling. This goes for all types of items from decorative objects to electronic items. Don't clear off all spaces though or it'll look barren. Experiment with the placement of objects to find a balance.
9. Try to get double duty out of decorative objects. The cat figure above is a lamp. The other item is a scented oil burner.
10. And, as a final overall tip... Don't try to accomplish everything at once. It's best to pick one area at a time and analyze it for efficiency. Perfect that space then move on to another at a comfortable pace. Generally speaking, you'll want to take advantage of "dead" (inaccessible spaces or necessary blocked areas) and inefficiently utilized storage areas while clearing surface areas. Analyze your shelving and how it is positioned and whether or not it suits the items you store. Sometimes a really narrow space (created by putting two shelves close together) is better than a wide one. Look at your heavily cluttered areas and work out what needs to be done to de-clutter them. Make sure everything has a convenient storage place.
If anyone tries these tips and has some "before" and/or "after" pictures, I'd love to see them. I'd also like to hear any other tips anyone has for living in small spaces.