As an open source project, we welcome new contributors and appreciate your help.
Before you start working on an unresolved issue or try to implement a new feature, please contact us via our public mapsforge-dev mailing list.
You may also create a new issue on Github or comment on an existing one to describe your ideas. We will then discuss the best way to realize your proposal and figure out how we can help you to get started quickly.
If you are only requesting a small change in the code, you may attach a patch file to the corresponding issue, but it is best to create a pull request on Github. Make sure that your patch is derived from the latest version in our dev repository, otherwise we might be unable to apply it. Please follow our code and style conventions. Detailed information about them can be found in the Project Conventions article.
Also please keep the pull request commits squashed, in order to avoid the clutter in repository and have only the finally changed files together. One way is described here.
Regarding syntax make sure your IDE uses for indentation 4 spaces (no tabs) and follow the conventions you already see in the code.
Please note that the mapsforge project is licenced under the GNU LGPL3 licence. Thus, all your contributions are going to be published under this license.