(Unorganized + ADD) * (Clutter) = MESS

There's not much we can say to help you. For documents, keep multiple folders for different kinds of documents, and use them. Never save anything on your desktop. Do the same with pictures, movies, etc. Keep your iTunes up to date, keep all album art, etc.

It's all on you. I don't have any real tips that could necessarily help you if you don't follow them.

 

Medication and therapy?

OP, You create the clutter that bothers YOU. No third party solution is going to help that.

 

What do you mean with "clutter"?

I have all my media automatically organized by iTunes, and my photos are being copied into the iPhotos library. Other than that, I basically only use two folders - Downloads and Documents. In those I arrange everything in folders and subfolders according to content. For instance if I'm looking for nutrition facts I will go to /Documents/Training/Food/Nutrition/

When I delete an app I will start with using their uninstaller, if any, I will then use the guide that's posted here on MR (do a search on the app's name, include system files, delete them).

Other than that, I let OS X take care of itself. I never use the desktop for instance, barely even know what I have as a background image

 

It is really the same as with a normal office, you put stuff in folders.
Use more folders and save it right there. Never save anything in downloads or to the desktop unless you absolutely intend to delete it very soon.
A downloads folder should imo never hold stuff that you miss if you just hit CMD+A and delete it all.
And the Desktop is imo something that magically creates clutter. Never use the Desktop for nothing but temporary stuff. Put no folders on it, put no files that aren't temporary on it. Just leave it a blank space. Don't even put to many links to apps on it.
You want order keep a clean desktop. It is the same as with a table you start putting one or two things there and not remove them immediately after work the mess stacks up. Windows of open application are what is some workstuff on your real table that you remove after it is done.
You never save something on your desktop. I only use it for temporary file copies.
That is I think the best solution.

Also don't do it like some noobs and clutter your dock. The dock holds the apps you use every day and the rest you should just access via Spotlight or Alfred. Some people have Photobooth, Widgets and other nonsense in the Dock. They probably think it looks smart because they have so many apps but it just looks stupid.