To increase the availability of Herb/Ore nodes within The Maw -
- Join a Maw Rep Farming Group (LFG)
- Phase in from Oribos
- Leave group
- Start farming
It seems that in the Maw, once you are phased in, leaving a group doesn't phase you out (correct me if this is wrong, but nodes remained present after I left group).
To increase the availability of Herb/Ore nodes in other Shadowlands locations -
- Join any LFG group pertaining to the area you want to farm in
- Help the group complete their task
- Wait for everyone else to leave the group
- Start farming
(The logic behind this is majority of the people phased into group maw instances are focusing on farming rep rather than herb/ore, so more nodes will be left for you to gather.)