I wrote a blog article on this awhile back on my blog HERE for Visual Studio.

However I will paste it here too:

How to use Visual Studio 2013

1. Recently Microsoft bought and re-released the popular Unity3D plugin UnityVS. The now renamed Visual Studio Tools for Unity plugin smooths the connection between Unity and Visual Studio and even allows one to perform debugging too! Download it here.
2. In Unity Editor go to Edit->Preferences->External Tools and In External Script Editor choose Browse from the drop down box.
3. Browse to and select C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\devenv.exe.
4. The External Script Editor should automatically show your selected editor as Visual Studio 2013.
5. That’s it! It should just work from that point on.