HoT where to start?
Go to the story journal in your hero panel. Activate the story in Heart of Thorns. Play the first story mission, because that’s how you unlock mastery tracks. Level gliding first, which is the default and go from there.
The first new zone, Verdant Brink, has day and night modes. Night modes are shorter and basically geared to defending encampments, in much the same way one defends forts in the Silverwastes. Daytime is different however.
Each daytime camp has it’s own event chain which you can follow through. Doing every event in the chain gives you an achievement and tells a story as well.
I’d level masteries in this order….gliding, mushroom jumping, updraft use and later on Exalted Lore.
Continue your story quests as you progress.
That’s how you start.