While no one is going to fault you for working at the family business, as an employer I am going to want to make sure that I am hiring someone who is good at their job, not just at collecting a paycheck from their daddy's company.
Some ways you can do this is to be able to talk about the work that you did in technical terms. (Warning analogy ahead) I do not really care what your secret recipe for making the donuts is, just that you know how to do what you do with that recipe, what factors you can change and what results those changes have on the donuts.
Also you need to be able to talk about what you see in your future. If you are looking to grow with the idea that at some point you will return to the family business with your new knowledge that is ok. Disclose that. If you have had enough of the family business, you need to be able to explain why, in a way that does not sound like you are airing dirty laundry, or talking bad about the business. If you do not know, that is ok to. But you need to be able to answer that question because it will be asked, and if you can't answer it then an employer is less likely to take you seriously.
If your father is on board with your expanding your experience, then ask him to help prep you for the kind of questions you should expect. He is likely the one that knows where your weaknesses are and can help prep you to over come them in an interview as well.
Also letters of recommendation from people you have worked with go a long way. And quite frankly a well written letter of recommendation from a father for his son that was also an employee goes a long way. He is not just saying it as your father but as a successful businessman.