Rule 1. Be extremely scared of the router... They are potentially dangerous tools.
I have mentioned the flying router bit that now (thankfully) resides on my neighbours roof and not in my body.
Rule 2. Be even more scared of the router as this will teach you respect for the tool. (see rule 1)
Rule 3. If you are blase about the potential life altering and physically damaging possibility of not respecting the routers ability to screw you up, see rule 1.
Rule 4. Refer to rule 1.