We recommend you first search among existing Arrow issues. The community may already address the same idea. If you could find the issue, you may want to contribute to the existing issue.
If you cannot find the same idea, you first need to write GitHub issues (e.g. issues in Arrow-julia) for a bug fix or planned features for the improvement. To write an issue would help the community have visibility and opportunities for collaborations before a pull request (PR) shows up. This is for the Apache way. We can use GitHub labels to identify bugs.
It should not be necessary to file an issue for some non-code changes, such as CI changes or minor documentation updates such as fixing typos.