In 2003, Harvard Business School associate professor Connie Bagley came up with these Top 10 Legal Mistakes Made By Entrepreneurs .  Some of these "mistakes" aren't mistakes at all if they are conscious choices, especially if you don't plan on seeking venture capital.  However, I was pleased to see Mistake #3 -  "Starting a business while employed by a potential competitor, or hiring employees without first checking their agreements with the current employer and their knowledge of trade secrets."  While I disagree with the statement that the law is clear that in every case an employee cannot operate a competing business, I do agree that this situation is a minefield that should be discussed with an experienced attorney.  Attorneys Peter L. Alteri and David J. Clark have prepared an interesting law journal article on this topic as it relates to New York law.

A qualified attorney will ask whether you are a key employee of your current employer, whether you have or plan to contact current customers of your current employer while still employed by your current employer (don't do it1), whether you are using trade secrets or confidential information belonging to your current employer (including customer lists), and other fact-specific questions designed to elicit whether you are breaching your legal duty of loyalty to your employer or other legal limitations on your ability to engage freely in your business.  

You should also be careful to review any agreements with your current employer, as they may contain a provision restricting your ability to compete.  The non-competition clauses are often unenforceable in Colorado unless they fall within very narrow parameters, but you probably won't know if you fall within those rules until you consult with an attorney.

I know you're busy starting or running your business.  But take the time to avoid these mistakes and you'll avoid spending time, money and effort trying to correct them later.