The most common closets you'll find in your home, office or other location are reach-in closets. Reach-In closets are usually of narrow width, shallow (2' deep) and whose height is the same as in the rest of the room. They aren't accessed by going into them (as in a small room) but by reaching in with your hand and arm to retrieve what you want.
Reach-In closets are commonly found in entryways, bedrooms, bathrooms, pantries and hallways for linens. They either have a conventional swing-out door, bi-fold or sliding doors. Sometimes it works best to remove the doors (especially in bedrooms and mudrooms) as they tend to get in the way and aren't closed much anyways.
The biggest mistake in outfitting a Reach-In closet is what builders have done in most homes--install a single pole and plank at medium height (usually about 68" above the floor). While this works for some applications, it doesn't utilize space to the best advantage. There are huge gaps below hanging garments (as most garments tend to be short as in a shirt or blouse) and above the shelf. Very typically over half of the space in these type of closets is simply wasted. A simple improvement (especially in an entryway) is to put an additional shelf above the hanging shelf.
Entryway: If there is enough width divide the hanging into long and double short. Usually one third for long is sufficient. Shorter jackets seem to prevail, especially for kids. So the double hanging works best for this. Configuring it this way makes for more total hanging space. Even if long or medium hanging is retained an extra shelf above the hanging rod and shelf will double shelf space. Also, a deeper shelf can be used with the hanging below it (16" vs. 12"). Another useful addition in these locations is a tower (either wire or laminate) with shelves to hold gloves, hats, scarves, etc. Using laminate, drawers and baskets can easily be added to augment the shelves. Small hooks can be fastened on tower ends to hang garments on. Many kids find it easier to hang their clothes on hooks rather than using hangers.
Bedrooms: The story is much the same in bedrooms as in entryway closets with only a single "pole & plank" installed. The result is that well over half the available space is wasted. Doing an inventory of clothes for a bedroom closet is a good idea. Very often little space is needed for long hanging garments. Bedrooms closets usually require space for sweaters and sweatshirts which are best not hung. Many men also choose to fold their jeans or pants rather than hang them. With these needs in mind, it 's wise to provide more shelves for folded items. Shallow towers are great for almost any bedroom reach in. The side walls of the towers can also be used for hooks or sliding belt and tie racks which retract out of the way when not in use.
Bathrooms: Even though you won't find a "pole & plank" in the bathroom, many bathroom storage areas could also be improved immensely. Shelves are either too deep or too shallow or more often improperly spaced. Again, little thought has been put into what needs to be stored and how much space it will require. If you are storing linens or towels, wire shelving works well. But if you are storing small items (such as medications or cosmetics), it's better to use solid shelves or have some sort of liners on the shelves so things won't fall through.
Pantries: No "pole & plank" here either, but the same situation exists here as elsewhere when no planning has occurred. Many special items can be added in pantries to help organize them better--such as lazy-susans, spice and bottle racks, under-shelf baskets, etc.