You do not really need to prepare the surface..but I recommend you clean the surface of the of any finger marks, dust, etc with soap and water if you can. This also cleans the mold release agent of the kit parts. The surface primer is basically the first step to preparing the surface for your basecoat as it will identify any imperfections on the kit.
I used to use Tamiya's surface primer as well as Auto Acrylic Primer. I now just prime my projects with either flat black or flat white tamiya acrylics. The flat black will give a pre-shading affect.