If you Google search previous RG postings in this regard, you will definitely get a clear idea. However, there are many more issues outside these rules. Consequently the position of the authors changes and often might not be to your satisfaction.

I suspect the order is subjective but I could be mistaken. This link may be helpful: http://www.icmje.org/recommendations/browse/roles-and-responsibilities/defining-the-role-of-authors-and-contributors.html

You might add an acknowledgment that defines roles, depending on word limitations and journal requirements. In meeting abstracts it may be effective to underline the corresponding author or presenting author.

either in order to contribution to paper or alphabetical by surname Occasionally it may be headed by team leader/senior researcher followed by other contributors in alphabetical order of surname

Thank you.