Design a 4 motor control board

Hi my name is Davis and I am looking to design my own programmable(Arduino code) PCB for my project. I am currently using an Arduino and an Adafruit motor shield(V2) to control my 4 wheeled robot. I do not need all of the pins for the robot, I just need enough for a 3 channel RC receiver and 4 motor ports. How should I go about designing this Board.

I didn't see this when originally posted. How is the degisn coming along?
1st step is usually capturing the design in a schematic, oftern you can copy the design of other open soource boards as a starting point, tweaking them up as you go, deleting unused bits, changing connectors, etc.
Then layout the resulting components as a board.
I use Cadsft Eagle for both, other software also exists.