~theme music for step 4~
Embrace the sandman within! Get to work sanding away those ugly corners. Not only will the board look nicer, but it will help it survive bumps and collisions later on in its life. While you're here, sand the top and bottom faces of the board as well. The final product should be a nice smooth surface all around the board. Like if I gave it to my baby cousin to suck on and she'd be ok smooth.
When you're done sanding, get a damp rag and wipe the whole board with it. This'll clean off all the tiny sawdust that blowing/brushing tends to miss ;)
You'll need a prepped surface for the rest of the design (woodstain/paint/bedazzleed jems)