I am quite new to this game and I am not sure how to ask people to be co-authors on a paper I have mostly written myself but that I think would get better with someone else's input. When is a good strategy to offer a coauthorship and when should I simply ask for a feedback on the paper? This is somewhat of a review paper and I feel that it would be important to have some experts from the field. But regardless how should I decide when to offer a coauthorship?
I'd ask for help. If said help turns out relevant, add a footnote thanking for it. If the help is in some way crucial (found and fixed a fatal flaw, suggested a (better) way to compute the results, suggested a relevant extension, ...) ask the helper if they want to be coauthors or just be thanked as above.
Co-authorship depends on many factors, few of them are:
- The authors who had worked with you together to achieve the results. Since this is your review paper, then co-authors may be them who had shared the knowledges to briefly summarize your findings to write the paper.
- To get the proper feedback of any research work mostly depends on the methods, results and discussions. So you need to find few researchers' paper which has a good overlap with your findings. Then you can ask the most focused/ experienced/ renowned researcher out of them to get some feedback.
- To increase the standard of the paper, you can ask well known scientists/ researchers who can reorganize your paper.