Understanding your audience comes before choosing your channels. Here's where to start.
Your ideal customer isn't a demographic. It's a person with a problem you're genuinely good at solving.
Start with the customers you already have. Which ones were a pleasure to work with, valued what you did and paid without a fuss? What do they have in common?
Then get specific about what was going on in their world when they came looking for you. What triggered the search? What were they worried about? What almost stopped them from buying?
That's the raw material for everything else — your website copy, your social content, the way you talk about your services. Get the customer clear and the marketing gets much easier.