I would suggest picking one field - either security or usability. While you may actually be an expert in both, it will be easier to position yourself as an exp

I would suggest picking one field - either security or usability. While you may actually be an expert in both, it will be easier to position yourself as an expert in one. This will make your marketing more straightforward. Then, you'll have to figure out how to educate your potential customers. If they don't know they have a problem, you'll have to teach them. Where do they hang out (online and in person)? Can you teach them why they would need your services and how you can help? Perhaps with a presentation or a whitepaper?