Do not add me as a friend and ask using the PM, all that I know myself or find on the Internet is posted here.
If the translation is not clear - write a comment! Part of it I translated myself, part of it was fixed by Dr.NTim.

Russian version:
http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=264153498

• Please note that officially* supported graphics card is not just with 1 GB of RAM, but all versions higher than nVidia GeForce GTX460 / AMD Radeon HD5850
  
• If game freezes on Ultra settings, try turning off the Vertical sync
  
• Disabling vertical synchronization can also help on the AMD cards.
  
• Sometimes fixing the config file helps: Documents/My Games/Watch Dogs/
  Open GamerProfile.xml and find DeferredFxQuality = "console". Replace "console" with "PC"
  
• You complain about errors and problems, but many did not check the system requirements, here they are:

Minimum:
OS: Windows Vista (SP2), Windows 7 (SP1) or Windows 8 (Please note that we only support 64 bit OSs.)
Processor: Intel Core 2 Quad Q8400 @ 2.66Ghz or AMD Phenom II X4 940 @ 3.0Ghz
Memory: 6 GB RAM
Graphics: DirectX 11 graphics card with 1 GB Video RAM - Nvidia Geforce GTX 460 or AMD Radeon HD 5770
DirectX: Version 11
Hard Drive: 25 GB available space
Sound Card: DirectX 9.0c Compatible Sound Card with Latest Drivers
Additional Notes: Broadband connection and service required for multiplayer mode. Supported Video Cards at Time of Release: nVidia GeForce GTX460 or better, GT500, GT600, GT700 series; AMD Radeon HD5850 or better, HD6000, HD7000, R7 and R9 series Intel® Iris™ Pro HD 5200

Recommended:
OS: Windows Vista (SP2), Windows 7 (SP1) or Windows 8 (Please note that we only support 64 bit OSs.)
Processor: Eight core - Intel Core i7-3770 @3.5 GHz or AMD FX-8350 X8 @ 4 GHz
Memory: 8 GB RAM
Graphics: DirectX 11 graphics card with 2 GB Video RAM - Nvidia Geforce GTX 560 ti or AMD Radeon HD 7850
DirectX: Version 11
Hard Drive: 25 GB available space
Sound Card: DirectX 9.0c Compatible Sound Card with Latest Drivers
Additional Notes: Broadband connection and service required for multiplayer mode. Supported Video Cards at Time of Release: nVidia GeForce GTX460 or better, GT500, GT600, GT700 series; AMD Radeon HD5850 or better, HD6000, HD7000, R7 and R9 series Intel® Iris™ Pro HD 5200

• Do not forget to check the graphics and other drivers for updates to solve problems with sound, graphics, etc.

Originally posted by NVIDIA v337.88 26.05.2014:

New in GeForce 337.88 Game Ready WHQL drivers

Game Ready - This 337.88 Game Ready WHQL driver ensures you'll have the best possible gaming experience for Watch Dogs.
Performance – Introduces key DirectX optimizations which result in reduced game-loading times and significant performance increases across a wide variety of games compared with the previous 335.23 WHQL. Significant CPU overhead reductions in the driver result in performance gains that will often favor CPU-bottlenecked situations. Per usual, results will vary depending on your GPU, system configuration, and game settings.

Install the new version of the driver from the official site is recommended NVIDIA[www.geforce.com], or through client software manufacturer, if it is already present in the system.

Originally posted by AMD Catalyst™ 14.6 Beta Driver for Windows® Operating System 27.05.2014:

Installing the new version of the driver from the official site is recommended AMD Catalyst latest Beta[support.amd.com], or through client software manufacturer, if it is already present in the system.

Do not forget to install and upgrade the following software:

• Download DirectX[www.microsoft.com]
  
• Download Microsoft.NET Framework 3.5[www.microsoft.com]
  
• Download Microsoft.NET Framework 4[www.microsoft.com]

Supporting the DLL:

• Download Microsoft Visual C++ 2005 Service Pack 1[www.microsoft.com]
  
• Download Microsoft Visual C++ 2008 (32-bit)[www.microsoft.com]
  ( Download Service Pack 1 [www.microsoft.com])
  
• Download Microsoft Visual C++ 2008 (64-bit)[www.microsoft.com]
  ( Download Service Pack 1 [www.microsoft.com])
  
• Download Microsoft Visual C++ 2010 (32-bit)[www.microsoft.com]
  ( Download Service Pack 1 [www.microsoft.com])
  
• Download Microsoft Visual C++ 2010 (64-bit)[www.microsoft.com]
  ( Download Service Pack 1 [www.microsoft.com])
  
• Download Microsoft Visual C++ 2012 Update 4[www.microsoft.com]
  
• Download Microsoft Visual C++ 2013[www.microsoft.com]

1) If the installation was successful, start the game - it'll start the installation and setup Uplay, if you don't have one installed.
2) Uplay runs itself (Log In etc.)
3) Uplay proposes digital key games. If Steam did not give the key to you in a separate window, right-click Watch_Dogs in Steam and choose "View Digital Key", then copy and paste it into Uplay.
4*) Also, in Uplay on the left will be a button "Unlock content" for Season Pass, do not forget to do it, if you bought Season Pass.

• Documents\My Games\Watch_Dogs\\GamerProfile.xml

• \Program Files\Ubisoft\Ubisoft Game Launcher\savegames\\0 or
  
• \Program Files(x86)\Ubisoft\Ubisoft Game Launcher\savegames\\0

Various error at startup, for example: "Executable file not found"

• Check CACHE
  
• When preloading:

1) Go to \Steam\SteamApps\common
2) Cut the folder Watch_Dogs in any place, for example: \Steam\SteamApps
3) Rename the cut folder
4) Remove the game in Steam
5) Rename the folder back
6) Cut and paste the folder Watch_Dogs back to \Steam\SteamApps\common
7) Install the game (Steam starts the installation, validation and will be installed with 0gb, but just visually, as it only loads the missing files.
Installed the other day:

• Try to reinstall the game, check the cache or perform operations above

If your card meets the system requirements, update graphics drivers.

If your card meets the system requirements, update the sound drivers.

Update the graphics driver, especially for AMD cards
Try running the game in windowed mode
or:
To avoid blue screen, we recommend that you update your drivers to the latest version (you can find links above), and then do the following: Open the properties of the system by pressing WIN+PAUSE/BREAK or by right-clicking "Computer" in the startup menu and selecting "«Properties» -> Advanced System Settings -> "Advanced" tab -> in the "Startup and Recovery" click "Settings" -> uncheck "auto-restart".

Disabling Mouse Acceleration (enabled by default):
1) Open the GamerProfile.xml with a text editor (location indicated above)
2) Set UseMouseSmooth to the 0
3) Set Smoothness to the 0
4) Save and close this file.

Error sometimes appears when you start the game through Steam, do repeated sync and everything should succeed

We can only wait until the game is released in your area

Restart Steam and check your regional settings

Reinstall DirectX

This error often happens on systems with graphics cards from AMD. You need to go to the Catalyst Control Center and go to the "Games" tab, then disable «AMD Radeon Dual Graphics». If you have several cards from Nvidia, try disabling SLI.

Download 3dmGameDll.dll (Google it). After that, unzip the file and put it in the "bin" folder, which is located in the root directory of the game.

Download isdone.dll (Google it). After that, unzip the file and place it at: C:\Windows\SysWOW64, while making the backup file being replaced. Restart the computer.
Click WIN+R (or «Start» -> "Run") and enter «cmd». In the window that appears, enter regsvr32 isdone.dll and press ENTER.
If you have enabled a tweak that switches the computer into "game mode", you should turn it off.

These errors indicate the lack of a specific Visual C++ package.

Errors of the same category, just related to the lack of the necessary DirectX files.

Right-click the game icon and select "Run as administrator".

This error occurs when an initialization program is running. Reinstalling Watch Dogs can help, preferably with disabled Antivirus and remote programs like Radmin and GeForce Experience.

Just like the previous error, the most effective option would be to reinstall your system, but try to (re)install all software (libraries and drivers)

If you have any unsolved problems, write in the official support service:

• Ubisoft Support (ENG)[support.ubi.com]

As well, it offers a solution and answers to some common questions:

• How do I disable Online Invasions?[support.ubi.com]
  
• How do I redeem my Exclusive Content code?[support.ubi.com]
  
• Where do I find my Exclusive Content for Watch_Dogs?[support.ubi.com]
  
• How can I change my in-game controls?[support.ubi.com]
  
• How do I exit multiplayer or quit a mission?[support.ubi.com]
  
• How do I launch into a public multiplayer game?[support.ubi.com]
  
• What are the minimum requirements for Watch_Dogs?[support.ubi.com]
  
• I am having trouble downloading my game from the Uplay PC Client. What should I do?[support.ubi.com]
  
• When I try to launch my game from the Uplay PC client, I am asked to enter my activation key again.[support.ubi.com]

http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=264153498