First: brainstorm, sketch, brainstorm, sketch, brainstorm, sketch...and buy a piece wood and cut it to size (it is always good to have that blank surface staring at you to give you that kick in the pants!)
Second: Scan the parts into the computer and begin the shuffling around in hope of finding the right composition. It has to feel right. If words are a part of the composition, choosing the right typeface is essential to the success.
Third: I did all my Photoshop designing to scale (27"x20" at 150dpi grayscale). I then chop the finished design into 8x10 chunks and print them out. The pieces then get trimmed and tapped back into a collage that looks like my final sign. I give a light rubbing of hard graphite on the back side of the collage. Tape it onto the sign board and trace it with a mechanical pencil which leaves a light pencil line to fill in with paint.
Fourth: Paint. I keep a few pieces of paper laying over the graphite so my drawing hand/arm doesn't smudge.
Last: I will coat the entire sign with a water based finish, Polycrylic (clear satin), to protect it. Before that is done, I will choose some sort of trim treatment to frame off the design.
I hope to deliver it to the boss soon since he's retiring after this school year. I'll take some shots of it when it hanging above the Office door.