Please read Tutorial for Unix first.

Install Mono

sudo apt-get install mono-complete

Install OpenCV 2.4.10

You must use 2.4.10. No other version is supported.

sudo apt-get install cmake libgtk2.0-dev libv4l-dev libavcodec-dev libavformat-dev libswscale-dev
cd
wget http://sourceforge.net/projects/opencvlibrary/files/opencv-unix/2.4.10/opencv-2.4.10.zip
unzip opencv-2.4.10.zip
cd opencv-2.4.10
cmake .
make -j 4
sudo make install

Install OpenCvSharp

cd
git clone https://github.com/shimat/opencvsharp.git
cd opencvsharp/src
cmake .
make -j 4
sudo make install