Issue reporting guidelines - git-for-windows/git GitHub Wiki
Search Existing issues & pull requests, both open and closed. Determine whether or not a bug report has been dispatched. What is the status of the report? Are there any other bugs to be looked at? If so issue another bug report.
Include the output of the git --version in addition to the Windows version as that information is often necessary to reproduce the issue. When reporting problems involving a server, include the same information for the server side (insofar possible). Likewise, please mention if you use 32-bit Windows, or a 32-bit version of Git on a 64-bit Windows. If in doubt, try to provide more information rather then less; It's better than leaving a lot of guess work! :)
Describe the options used when installing Git for Windows, and the console type/window (if any).
If your setup is different from "normal" setups in any way, it is a good idea to put specifics about that into your bug report, too.
Describe your issue properly. If you spend 30 seconds throwing out a sloppy report, do expect that others will spend exactly the same amount on trying to resolve it. In contrast, if you write a complete and pleasantly informative bug report, you will almost certainly be rewarded by excellent help with your problem.
If your issue stems from a particular repository include its URL. If the repository is proprietary try to create a public test repository showing the same issue.
Be prepared to test fixes!
Be polite. You are asking highly competent software developers for help, for free, so you might want to avoid treating them as if they were a commodity or at your free disposal.
An example for an outstanding report can be found here. You may want to imitate the level of detail.