Establish an online presence, and start local. Identify gaps that exist in the content strategy of local businesses in your area - 'ma and pa' type shops are a good place to start - and approach them directly, with a clear and concise value add.

Small businesses are budget conscious, so they need to know exactly what they're getting for the money they're spending. If you don't have clear and tangible metrics that can demonstrate the success of your past work, it's definitely worth ironing that out a bit more. ie. What was the open rate of your email marketing strategy; the click-through rate, etc? How many impressions, engagements, conversions, etc?

You also mentioned that you don't have any previous customers or testimonials to offer when pitching your services, which could hinder you. It may be worthwhile to either ask your previous employer for an online review, or offer up a few pro bono projects to friends/family in exchange for a testimonial. Ideally you'd have these listed online for prospective customers to view, along with a sample of your work.