In hopes that it will help with the crashes and "not-working" problems people seem to be having, I will update this list with tweaks and hopefully fixes, as i find them.

1 - Check the requirements.
First of all, and I can't stress this enough, The Witcher 3 is a next-generation game in every sense of the word. That means it will not run on old versions of Windows and/or old hardware. If you somewhat get it to run on these, you will surely run into problems sooner or later.

- The Witcher 3 requires 64bit version of Windows, this is one of the biggest reasons for all those "wont run" problems. As far as i can tell it can't be ran on 32bit (probably won't start at all).
- Make sure you have at least a quad core (4 cores). I have read people have gotten it to run on Core Duo, but with a lot of problems and not to mention lag.

2 - Ample memory
- Make sure you have at least 6GB of system ram installed. If you have less, the game will run but you will get crashes fairly often.
- You will also need a graphics card with at least 1GB of vram. Don't even try to run the game on anything less, you'll end up punching a hole through your monitor.

3 - Install the redistributables.
There is very little information on the internet about this, probably because everyone should know it already.
- Every PC game in existence requires one or more redistributable packages, be it DirectX, Virtual C++ etc.
Witcher 3, as far as I know needs these.

- Install vcredist_x64 and vcredist_x86 (https://www.microsoft.com/en-us/download/details.aspx?id=40784).
- Install nVidia Physx, yes even non-nVidia users (http://www.nvidia.com/object/physx-9.14.0702-driver.html)
- Install or update directX 9c (https://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=35) - Windows 7 should already include it, but install just the same.
- Install or update DirectX 11 (https://support.microsoft.com/en-us/kb/179113).
- You should have it already, if not, install KB2670838-x64, NO exceptions (https://www.microsoft.com/en-us/download/details.aspx?id=36805).
- You should already let windows update and install these automatically, but if you do not, it's probably a good idea to install NET Framework too.

4 - Update your Graphics Card Drivers
It goes without saying that you should update your graphics card drivers periodically or in case of AMD users, as they are released ( every 5 years?)
- For nVidia users (http://www.nvidia.com/Download/index.aspx?lang=en-us).
- For AMD users (http://support.amd.com/en-us/download) -- I have also found this unofficial beta driver to give a slight FPS boost (http://forums.guru3d.com/showthread.php?t=399245), it's safe don't worry.