New functions should be developed against latest development version in "master" branch of the official git repository at https://github.com/OSGeo/gdal).
Contributions are preferably proposed following the usual GitHub workflow and submitted as pull requests against the latest development version in "master" branch of the official git repository at https://github.com/OSGeo/gdal).
Please, submit new pull request with a new driver code, driver test cases, changes to the building configuration required for the new driver, etc. So, we can track all necessary updates and changes in one place. After a new driver is incorporated and well tested, we can annotate and close the pull request.
Code contribution shall be done under the MIT/X license in order to be incorporated into GDAL/OGR baseline. Refer to the Legal paragraph of RFC3 for more details.
Subscribe to the mailing list and answer questions where you have gained some knowledge (and everybody knows something!).
Contribute to the wiki, improving documentation, providing examples, etc.
File quality bug reports using GitHub issues at https://github.com/OSGeo/gdal/issues/new when you observe errors. The greatest value comes from boiling down the problem to the minimum manifestation with small data files such that a developer/maintainer can very easily reproduce the error.