Tranquility generally follows the same contributing guidelines as Druid. See here for Druid's guidelines: https://github.com/druid-io/druid/blob/master/CONTRIBUTING.md
The Druid intellij_formatting.jar contains a Scala codestyle as well, which you can use to ensure your Scala code is formatted according to project conventions.
The Druid CLA applies to Tranquility as well. Please fill it out when contributing to either project. The same form does apply to both projects, so there is no need to fill it out twice.