We have found the following:

1 Using the API is better than waiting for Google to crawl the jobs.
2 They have you must have data fields, but they have would like to have and be tickled pink if you have fields. Filling in all three changes rankings in the testing we have done.
3 The quality of the title you give vs the title they understand.
4 The overall authority of your site. No exact on this yet but a gut feel factor.
5 SERPs result are also jumping around like crazy just now, we see the Google for jobs panel with no links about it and then four hours later it has 4 organic links about it for the same search, then a day later 2, then a day later none, then back to four then an hour later none...

Testing google for jobs when it landed in the UK three weeks ago its results are inconsistent with its own rules, we have found jobs with the wrong suggested title format, the wrong address format, landing pages not actual jobs have found their way onto the service!!! jobs with red warning have made it onto the service and so the list goes on.