A product from Google will take real effect in their search engine. I think Google Plus submitting is not the best, but one of the must-have work in SEO.
Search for some tutorial in Google, start with basic skill like on-page SEO method, keyword research etc, then provide your skill with off page SEO, or even black hat SEO technique.
Stop targeting keywords/ marketing channels which are sending low-value traffic, and try to adjust in-page factors that can effect visitor's experience, like page load time, relevant content, pop up etc.