I did a book review on startups recently. Although written for businesses, much of the content is applicable for people thinking of starting a nonprofit. It encourages you to really research whether or not there is market for your service which is as important for non-profits as it is for for-profits.
Is your organization intended to meet a specific need that another group is already meeting? If so, perhaps you can partner with them instead of trying to start something totally new. Or maybe your organization is needed because it serves a very different geographical location. Ask yourself these business questions before you get too involved with the work of starting a brand-new 501(c)3. Consult with for-profits as well as other non-profits as you put a plan together.