How to guide new contributors?

Hi, I think this is a interesting reflection, I've always asked myself if I'm doing things right and if I'm providing them (the new mappers) the right tools to start mapping things the right way.

• Usually I don't really welcome other mappers, the only time I do it is when I see their changeset/s contains errors (deleted objects, mistakenly moved nodes, added fictional objects, and stuff like that). When I add a comment to a changeset I do try to explain him/her the errors and pretty much half of the times I do get a really kind reply and friend request.
• Deleted objects, non squared buildings, names tag used to point out the object's category (eg. a node with name=viewpoint instead of tourism=viewpoint), nodes moved hundred meters from their correct location, overlapping objects (road over building is the most common) and nodes like restaurants, placed on the sidewalk instead of on the building in which they are actually located. I'm pretty sure I forgot some other errors. How do I point them out? with changeset comments, I do add a lot of comments, I think changeset comments are a super powerful tool as the new mapper receives a email when I add a comment and today everyone uses to check his/her email almost daily.
• 99% of the times I do explain him how to fix his errors and I do also ask him to fix it by himself and then I do double check his/her correction. I do correct errors without waiting for and answer only when those are pretty big errors. Expect me to immediately revert your edit if you delete the Duomo di Milano in Italy :D I do so because I hope that after my explanation they're not going to make this error again, if I fix it by myself instead, they're not going to learn how things should be done. So far I think my method worked pretty well.
• Actually they don't use to ask much. I do use to link them the wiki main page and learnosm. I'd like to link them the editor integrated in iD (but so far I didn't find a way for doing it), because I do reckon that most of the times their errors are driven by the fact that they're not familiar with the editor.
• That's a difficult one. I'd say something in between 10% and 20% of the ones I did help out actually contributed few tens of edits