Beginners Guide 1.4.2
Uploading your changes to OSM
Most editors will prompt you to enter changeset comment:
- JOSM among many tools on changesets, additionally exposes manual handling of conflicts
- If you haven't uploaded your data longer than several hours or days, you may want to update your data using update tools Update Data Update selection Update modified to lower chance of conflict. You cannot avoid conflict if data modified by you was quickly altered by someone else before you uploaded your changes.
- (optional) more materials on conflict handling in JOSM:  
Split your uploads to areas of reasonable sizes and relevance
If your edits are over vast distances, you risk the bounding box of your uploads to become huge! For Quality Assurance and reviews, seasoned mappers worldwide suddenly get flagged about your upload, although your nearest upload to them might be thousands of km far away and none of their concern. To avoid this unwanted behavior, split your uploads please. I.e. before moving on to edit in another city, municipality, province or country please upload your changes first and then you continue mapping in the other area.
Testing your changes before upload
If you like, you can load your changes into another OSM-based application to perform testing beyond whatever is possible in your editor, so if you find problems, you can fix them before uploading. There's no general expectation that contributors do this; it's understood that contributors will sometimes make mistakes and they can be fixed later as needed.
- Good changeset comments - (optional) will cover why it is important to comment changesets