Step 1: Design your box layout
For my purposes I opted for two rows of three, with the row at the back being quite a bit longer than the three at the front so they could accommodate the longer cutlery in my silverware set.
I bought some nice looking 1/4" sanded plywood and calculated in 1/4" inch for each box edge and divider. I was surprised later when I went to piece together my first prototype and discovered that the wood was not actually .25" but was .2" (much like 2X4 boards are actually 1.5X3.5). Be sure to measure the actual stock you're using so you don't get fooled by nominal sizes!
Some design considerations:
1. Having deep, narrow sections makes it hard to get to the bottom of the caddy when you're fishing for the last few pieces of silverware. Consider cutting a notch or lowering the height of the middle of each divider so you can easily grab your silverware.
2. Having some space along the side of your caddy can be convenient for storing odds & ends (like a pair of scissors). If you decide to make the outer border of your caddy smaller than your drawer, it may be worth making the bottom piece extend past the sides of the box so it touches edges of the drawer itself, acting like a spacer to keep the caddy from sliding around.