How about starting a website for your business. It is good for exposure too and make people know your business.
Build A Site For 3 Bucks - Build A Site
Nice to hear about your interest generally people never think about starting a new business in the age of 18 but you want to do it even you are doing another business with your partner also this is really very good thing. I want to say that it depends on your interest that which type of business you want to start apart from this you must have knowledge about a business before starting it. If you are thinking to start an online business then you must have strong network or clients who will provide you project.