First you need to sign up as a google product search partner and submit your feed and then you are work on optimizing your products.
There is some good piece of advice. If you want to see a certain product in top #3 position, for example, try to spend some time to this issue, log in Google shopping product search, choose the most appropriate category for the product, add the product information (do it very thoroughly, because potential future clients will read this info and will make a decision to buy it or not). And this is pretty much everything you need to know to promote and sell specific product.