I need to rank higher on google maps

We need a strong strategy to bring our exposure on google maps in line with that of our main competitors. Our review level is about the same, but our frequency of top five appearances in searches seems very low. I don't know if this is because we advertise on adwords a lot. I understand that such appearances used to be down to physical location - in our case, proximity to town centre, but now it has more to do with online credibility - back links to site, appearance on other online review sites, etc.