Selected answers from the Dumb SEO Questions Facebook & G+ community.
Tony McCreath: I will start with the two obvious ones: location + relevance.
Most people talk about getting citations to help it rank. That is getting the Name, Address and Phone number (NAP) cited in as many places as possible. E.g. local business directories.
It should be noted that if the url your places listing uses also ranks in its own right, then it gets merged into the places listing and this may help it rank better.
Ranu Jain: Google places listings search results are based primarily on relevance, distance and prominence. ;
Relevance: Relevance is how well your local listing matches with the inquiry someone is searching for. A complete and comprehensive listing in Places will definitely rank better on SERPs.
Distance: It is how far is each potential search result from the location term used in a search? If you don't specify a location in your search, Google will calculate distance based on what they know about your location.
Prominence: It is how well-known or prominent a listing can be. Google gathers this information from links, articles, and directories related to your listing. Some places are quite prominent in the offline world. Google tries to ;reflect this online as well. For example, famous museums, hotels, or renowned ;store brands that are familiar to people are also likely to be more prominent in search engine result pages.
Justin Y: I think it also has to do with quality too, on top of having a verified page with plenty of citations. Having good reviews is always plus and having negative reviews may count against you when competing with nearby businesses.
Not always do people do local modified searches, narrow their search to nearby results and nor is Google always right about identifying the users exact location.
My suggestion is to stay on top of your reviews, have a verified page, enough citations, and make sure that your page is optimized and relevant to your location.
Ian Dixon: Google manages some very weird things on where it thinks somebody is though +Ranu Jain ; Just look at my location in my profile which Google filled in for me at some point. I'm a closet plain spotter who lives at an airport. They send me ads for ice cream in Brighton. Nope I dont live there either gMail gives me ads for local services in Clapham. Dont live there either. Tried ip2location to see where I was today Crawley and I dont live there either
I've bever confirmed this but my belief is that a lot of this information is based on where an ISP says an IP address is and the ISP will move the IP addies around without updating the location. Things may be different on mobile with the possibility of using GPS to better identify location
Mark Gilvey: And again, the need to nurse customers to get them to write reviews appears to trump everything.
What affects your position in the Places listing? 
