I am using this web site for this article.
Open terminal (ctrl + alt +t), and write:
1. sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
2. echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
3. sudo apt-get update
4. sudo apt-get install mono-complete
5. sudo apt-get install monodevelop
6. monodevelop
Now you should see screen of MonoDevelop...