I always keep in mind to try and make sure the electronics are protected as much as possible. Heatshrink over ESCs helps. I used to wire-tie them to arms but wire-ties can crack an ESC in a hard crash, so now I just wrap em in PVC electrical tape a couple of layers. Some even recommend cutting old prop blades to fit over the ESCs before taping over them (this adds weight to your quad though - but protect them from running props, should they breakaway and fly off during a crash). Make sure your wires are tucked in nicely and have enough 'slack' to give at the solder joints, so they won't crack when the frame flexes on hard impacts. Put silicon rubber cement over FC/ PDB or 4-in-1 ESCs (if you are using those) wiring/ solder connections to protect them from shorting with each other (this also adds weight). Protect your batteries from impact as much as possible (use dampening rubber gripping pad material or similar - one good recommendation I found out by googling is to use bicycle rubber tubing). Most of the suggestions add a little weight to the quad. If you are a racer, you will want to keep your quad as light as possible, and those tips may not work for you. Sometimes winning for racers means taking a risk by not protecting the delicate items onboard the quad, just to keep it lightweight as much as possible.