A beautiful room is a well-organized room.
It doesn't matter how fabulous your design is if it's trashed with kids' toys, piled with papers and magazines, lost under laundry, or drowning in knick-knacks.
A room must function for the way you ACTUALLY live, not for some fantasy life you think will be delivered with your new furniture, and for that to happen, the organization needs to be built in from the start.

• If you have kids, you have stuff, and that's ok.
  What's important is that the things they have are things they USE, and that storage space is provided to accommodate them.
  Unless the room you're working on is a play room, don't try to house everything they own in one space.
  Rotate the toys throughout the house, and they will aways feel like they have new things to play with - giving you more mileage per item (and per dollar)! Plan some toy storage into each room, the size of which will dictate how many can be kept in a given space.
  
• If papers are your demon, the best answer is to learn to handle them more efficiently: Mail and documents should be dealt with the first time you touch them.
  File, sign, review, shred, recycle, or pay them immediately, and you'll never have to scramble to find them at the last minute (or worse, when they're already late).
  
• Collectors of magazines, catalogs, and newspapers, you have a little soul-searching to do:

1.
Why are you hanging on to these items? Good articles? Inspiration? Things to purchase? Keep in mind that much of the information in these sources expires...
that's why they're called periodicals.
2.
When is the last time you referred back to an old issue? When you tried to refer back, were you able to find the article / recipe / ad / information you were seeking? How are you keeping track of what's in each issue? Do you really need to keep the ENTIRE issue, or would it be more efficient to clip the items you wished to save and store them separately? I suggest you really think about each of those questions.
If you're keeping periodicals for reference, you MUST have a system for accessing that information, because if you can't find it, you may as well not have it! Next, assess the storage space you have available.
How many issues can you reasonably store? Set a limit, and when it is reached, begin clearing from the back end, and show no mercy!

Clothing can be the bain of the bedroom (or bathroom...
or laundry room...
).
As with the papers and periodicals above, you must have a process for handling the laundry as it comes through, and sufficient storage space to hold it.
If laundry is a routine problem, you are missing one of those two things.
For most people, the primary issue is simply that they have FAR more clothing than they could ever wear: skinny clothes, fat clothes, work clothes, play clothes, dress clothes, memorabilia clothes...
you name it!

I walk my clients through this process in far greater detail (and with a lot more hand-holding), but this is the exact process for paring down - in plain English: 1.
Take a look at what you own.
2.
Take a look at your available storage.
3.
Take a look at what you actually wear.
4.
Get a box and start donating, until what you own is equal to or (preferably) less than your available storage.
5.
Reorganize your storage space such that putting away your clothing on laundry day is a snap!

• Knick-knacks.
  Memorabilia.
  Tchatchkis.
  Collections.
  Call them what you will, when they get out of control, all you have is clutter.
  

On the one hand, these are the personal touches that can bring a room to life, and fill it with the personality of the inhabitants.
On the other, there is a right and a wrong way to use them.
I often enter homes to find surfaces covered with family photos in mismatched frames, or tiny memorabilia pieces picked up on travels, or just general STUFF with no rhyme or reason whatsoever, except that the owner didn't know what else to do with it! Accessories are an important layer of a well-designed room.
They should enhance its character and inspire curiosity or conversation.
That's a challenge when you can't see the forest for the trees! To solve this problem, remember the rule of 3's and 5's.
You want to cluster object together in odd numbers, usually 3 or 5, on an individual surface.
They should somehow relate to the design of the the room, and they should be of varying sizes, so each can be seen easily.
If you have a group of like-sized items, raise some up by standing them on books or boxes, making them taller than their neighbors.
(This is also a great way to sneak in a couple extra items without creating more clutter!) Also, try to group like items together to give your collections more power and impact.
At OnlineHomeDecorating.
com, beautiful accessories are included with every design, as well as instructions on how best to display them - no guesswork, and NO clutter!