Welcome! While this leveling guide is specifically made for the class and specialization(s) listed, we also have a general Battle for Azeroth leveling guide that focuses on the specific features of the Battle for Azeroth expansion including preparation of your mission table that will be used to unlock new areas, progressing on your faction's War Effort to save time at Level 120, and a reminder to keep ALL of the gear you find for the Scrap-o-Matic 1000 or Shred-Master Mk1, which will greatly increase your resource generating capabilities. Please visit our 110 to 120 leveling guide for this information and more (including Heirloom and War Mode advice that also applies to players who are not yet Level 110.
Pick druid, paladin or monk. Get heirlooms if you can. Grind mobs until level 5 - 6. Start doing the easy "just kill these mobs outside town" quests until 15. Queue rdf as every role and do every dungeon you can (with heirlooms you could probably solo the dungeons) while you travel to higher lever zones. Keep doing the simplest quests while you're waiting for rdf (which shouldn't be long). I leveled a druid to 100 once doing this in maybe a day /played, but he was also rested for most of the process.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.