The last thing you want to do is spend months or years building a product and a company, only to find out that you didn't really own the intellectual property you thought you did. That problem can kill a company! To make sure that doesn't happen, talk to an attorney about the topics raised in the "Protect Your Intellectual Property" section.
And talk to an attorney about any non-compete and ip-assignment agreements you have with prior employers.
And finally, when you leave your job to start your company, be sure you take nothing with you that belongs to your employer. And again, talk to an attorney to make sure you're clean!