I think original, attractive and fresh contents would be the essential issues for any successful blogs. Also, you would need to promote your blogs online via channels like social media, niche relative forums, press releasing and others.
If you are looking for someone to market your blog then I would be happy to do it for you. I currently own 4 blogs and I am sucessfully marketing 7 Blogs for my clients. If you would like additional information please let me know.