Recently many Qubes OS open issues are marked as “good first issues” on Github by some of core-team devs.
These issues are usually very easy to fix. Sometimes less than 10 lines of code or even just an updated comment is sufficient to resolve such issues. Early contributors interested on contributing to Qubes project are encouraged to take a look at them. Some of the solved ones or open issues which have received pull-requests are good examples on how to solve such issues.