An agency owner’s first hire should be a hire that can handle things that are outcome independent. This means that it doesn’t matter who does them, the outcome is the same. This is very similar to outsourcing. Find pieces of your job that you don’t actually bring any unique value to, for instance, pulling reports out of Google Analytics. You are no better at downloading that Excel spreadsheet than anybody else. You don’t click the button with any more flair. It doesn’t download any faster. The results are not different, so you can hire someone to do that.
As an agency owner, you are probably in charge of everything. You’re in charge of selling, and financing, and delivery, and client management. You have to start taking stuff off your plate because as awesome as you are, you are not equally good at everything. You need to start taking the things off your plate that don’t actually matter. The first hire should be the person who is happy to take over those outcome independent things and own them.