The best thing would be to not have a non-compete agreement at all. Failing that, you should try and limit it as much as possible in geographic scope and in duration. Limit it narrowly to the area the employer is really concerned about you working in - not the whole industry or line of work. For instance, you might ask that the limitation is to the area of clothing retail if you work in a clothes store, versus retail generally, which would cover a very broad range of possible jobs that are truly unrelated. The goal is to limit the agreement to what is necessary to protect the employer. You should also consider asking for severance pay in the event of an involuntary termination.
Whether an agreement is likely to be valid depends greatly on the analysis of state law as applied to the specific facts of you and your employer's situation. With so much potentially at stake, if you have any concerns at all about an agreement, it would be wise to consult with a lawyer who is familiar with these types of agreements. Guessing wrong about the validity of the agreement could seriously affect your ability to work and could cost you a lot of money, so you want to proceed carefully.