Last thing we did was grab some stick-on felt and put that on the bottoms of the pieces so that they can't scratch the plexiglass all to hell. That'd ...
Step 13: STEP OF DOOM!
Next thing to do is to pre-drill a hole for each screw in the board itself. You want it to be a very small hole, since screws can dig their own way in if they need to. Basically, you want the drill bit to be about as big as the screw MINUS THE THREADS. This is important enough that I made a separate step, with just one picture for it.
And so of course, the picture sucks. Such is life.