Start with who are your potential clients? Do you have a previous niche/area of expertise that you can write about? It is much easier to sell yourself in an area you are proven in. Or if through PPH you have developed an expertise in a certain area, what other orgs would be interested in buying those services? Who is it that usually commissions you? A marketing person with no time, a PR person?
Then I'd tap up ex LinkedIn contacts, get on social media, get out networking and make tailored approaches to likely clients. Follow other writers that appear to have developed their niche.