It has been asked before Seyed, as identified, but I will succinctly highlight my practice. The corresponding author is the main contributor (in the case of Higher Degree Students this will always be them). The last cited author is usually the 'consultant' expert - but not always. If there is no 'consultant' then it is the 'least' contributor (that's the dilemma with final author). Authors in-between are listed according to their contribution - highest to lowest. All contributors have a place - including Research Assistants. Admin support, advisers etc can be identified in acknowledgements.