Very quick checklist:
1. Fill out a complete profile. Provide as much information as possible, including pictures, video, etc.
2. Wait. If you have not previously claimed the listing you'll need to wait for the snail mail PIN to confirm.
3. In the meantime...be sure the business is listed in as many business directories (InfoUSA, YP, etc.) as possible. Google will reference these. Be sure the business name and address are exactly the same everywhere (Website, Google+, business directories).
4. Solicit positive reviews. Yes, you can try to get these done on Fiverr or other services, but Google is getting good at finding shill reviews. Depending on the business you can ask for the review at the time of service (provide the customer a computer or iPad and offer a discount for a good review).