Second, make sure your legal documents are in order. Incorporate, if you haven't already, and open up a business bank account. Make sure to use your business bank account for all business related expenses. This will make accounting much easier down the line.
Third, hire a great bookkeeper. Trust and loyalty is really important here, so best if you hire someone who is somehow connected to you.
Fourth, hire a great accountant. Some accounts will also do bookkeeping for you. I don't think this is a good idea, as you typically want someone "on your side" watching out for your day to day finances. Intelligence and industry expertise is really important for an accountant.
Fifth, if you're making real money, it's important to put some words on paper about how the company ownership is divided, and other "what if" scenarios. You typically also want some sort of Operating Agreement between the founders. Usually this document covers: 1) ownership division 2) provisions for terminating members 3) provisions in case of long term disability or death of a member (for example, do you all of a sudden want your cofounder's spouse or parents as your cofounder in case of death? Look into "key man" insurance.) 4) provisions for adding new members
Some people say get a lawyer for these documents, which isn't a bad idea, but most of these types of documents at this stage is pretty boilerplate. If you have some unique circumstance, like an international cofounder or something like that, then perhaps consulting a lawyer is best.