I recently started a new business with 3 other partners. Myself and two of the partners had worked together in a previous business and knew each other pretty well. We all thought our strengths and experiences complemented one another...but problems began almost immediately...
Make sure your partners are honest and in agreement. Private conversations that portend problems need to be brought to the attention of everyone.
Make sure you have capital in place, don't spend before you have good solid plan, revenue and agreements in place.
Meet regularly to share ideas and update everyone frequently