I've been writing an employee handbook. It's a dull and thankless task. But I suspect it's going to be one of the most valuable things I've done in a while.
I've written before about drawing up an organisation chart for your business. Even though you probably fill the majority of the roles on it.
Drawing up an employee handbook is the next step. As you do the jobs yourself, you should be able to ask yourself "when I'm being the Managing Director/Sales Executive/Chief Tea Brewer, what do I have to do every day? Every week? Every month or quarter? What else is my responsibility".
Write all that stuff down - a page for each role.
Because when it comes time to hire - you can use that to put the perfect description into your advert. And when you find the right person, you'll be able to explain to them exactly what it is you want them to do.