* Do this on your own time. Maintain separation and document as necessary
* Make sure that you did not sign anything as part of your employment agreement that claims ownership over your ideas, thoughts, inventions, data etc. outside of working hours
IANAL2 (but I read a lot of contracts), here are a couple more:
* Read your assignment of inventions agreement _very_ carefully.
* If you live outside of California check your employment agreement for non-compete provisions.
If in doubt consult a labor lawyer. Getting qualified legal advice when starting a company is worth the money.
* Do this on your own time. Maintain separation and document as necessary
* Make sure that you did not sign anything as part of your employment agreement that claims ownership over your ideas, thoughts, inventions, data etc. outside of working hours
* Do not use any company resources