In order to maintain a constant position on SERP ranks, it is essential that you updated your blog with unique content on a regular basis. Try building organic backlinks from sources like Social networking sites, forums, communities, increase the presence of your website through Social Bookmarking, Twitter Updates. This is provide a steady growth in your site's ranking.
We have to keep on update our website or blog. whenever Google index, it will understand that this particular website in use. if we don't update our website automatically the SERP will come down.