To become an entrepreneur, you need strong sales skills hence working in sales would really help. You can have a great team, culture, funding but without sales your start-up would eventually be dead in the water. If you have strong sales, rest of it can be set-up or brought in gradually. Whatever field of business or industry you have a passion for, or already have plans to enter with your own idea, you should work in that field as a sales guy. Sales gives you an idea of the market, give you time to interact with and understand the customer needs, wants and price points. These are the number one skills required when you start your own venture.