In order to build a virtual image of professionalism for your blog, you need consistency. Go with your brand and identity as it should reflect in your design, logo, colour code etc. Write useful, well-crafted content that speaks to your core audience and establishes you as an expert in your field. Be professional in your tone, but build relatability. Remember to have some conversations in the comments and on social media with your readers. Lastly, add a professional website layout and possibly custom domain to accomodate a potential credibility benefice from your blog posts.