fresh level 50 - start doing some dungeons until they start getting some tomes and get some mythology gear from doing story mode dungeons.
Step it up to do some HM dungeons once they have at least geared a bit better (not much but don't literally want a completely fresh lv50 in HM dungeons)

At this point - Mix it up maybe do some Crystal Tower if they wanted a little change and to get some ilvl80 gear however they can do this or HM dungeons but can't just step into CT either until at least picked up a little mythology gear) (CT needs more of a soldiery reward to be honest as its longer to run than a HM dungeon but another story for another day)

Once you have a mix of 70/80/90 gear might then want to do HM primals and start working towards relic and then +1 but again need at least an ilvl that is fair even if it is easier now than it ever was with echo and such people should still progress properly.