The 'Dungeons' tab on the 'Classic WoW Planning' spreadsheet is probably the best place to start:
https://docs.google.com/spreadsheets...#gid=566752830
The list gives you the general consensus, mainly from fellow boxers, on which dungeons to run in which order by level range and faction (where faction matters). Various sources are linked that may be helpful for context/background.
Guides for the dungeons can be found via the orange highlighted link at the top of the sheet.
Maps for the dungeons can be found via the green highlighted link at the top of the sheet.
XP info for the dungeons can be found via the fuscia highlighted link at the top of the sheet.
The 'Levels' tab in the spreadsheet gives some perspectives on the instances as well.
The 'ToDo' tab in the spreadsheet has various links for things like World Travel (how to get to a given instance, etc).