Optimise google feed for opencart store

Hello. I have an opencart store, and i want to get the google feed and my google account optimised for the google shopping engine. I want to start appearing at the top of the google shopping results, so need it setting up properly. The feed is already set up, and registered with google, the products are on there but im not getting any clicks. I also have the following problem coming up. Missing recommended attribute: google product category (52 warnings) While items missing recommended attributes will process successfully, we recommend including relevant attributes if they are available. Please only bid if you know hwo to get the feed optimised so that my products get to the top.