One thing I learned transforming from an employee to an entrepreneur, was the importance of maintaining and developing professional relationships. A former relationship from your old place of employment could very well lead to a new, financial business partner or a longterm mentor. Who knows? You don't, so why risk destroying relationships with coworkers of managers from your old position?
If you're like me and you have left or are leaving you corporate job to start your own company. you should absolutely keep one foot in the door of your old gig. Most likely, you spent time and put effort into creating and developing personal and professional relationships with people you worked alongside or beneath. These people could be future allies down the road, or future employees in your start-up.
I've listed a few ways to take advantage of your former networks below: