This instructable will attempt to provide the basic design principles, resources for obtaining the necessary tools, and some of the traditional rules of making a beautiful and delicious bento.
Step 1: Know the rules (then break them!)
The 4-3-2-1 rule: 4 parts rice, 3 parts protein, 2 parts vegetable, and 1 part "treat" (Usually either pickled vegetables or something sweet.)
Sushi should be prepared with more wasabi than usual.
Pack foods with flavors that might run or stick together with a divider. Separate wet foods from dry using a nested or altogether separate container such as a cupcake form. Sauces and dressings go in their own bottles (usually with a lid or cap).
Oily foods (like gyoza) should be packaged on top of an absorbent material.
Bentos should not require refrigeration or heating.
Above all else your bento should be equally as nice to look at as nice to eat! (Note that this is the only rule that is not optional! :)