Google has rolled out a checklist for improving mobile websites..
The list comes in three steps:
For step one, there are tips related to removing extra windows from all mobile user-agents, providing device-appropriate functionality, testing, etc.
For step two, tips get into ptimizing crawling, indexing and the searcher experience and optimizing popular mobile persona workflows for your site.
For step three, tips are about considering search integration points with mobile apps, investigating/attempting to track cross-device workflow and brainstorming new ways to provide value.