1. Objective of it really depends on the player's interests. It can solely to complete the main story, and not much else. It could be to complete all the quests in every zone including exploring to find the hidden quests. It could be exploring to fill the codex, and so learn the lore of Thedas that way.
2. For what to do next, other then the main quest chain it is rather open. Usually I follow where the main quest chain leads, so for example: Adamant takes me to Crestwood, so I finish that zone before moving on. Then it takes me to Western Approach so another zone to do before completing that particular main quest. Generally just by reading the quests, and noticing what the specific zones have (enemy levels, rift levels, theme of the zone and it's main quest) points me where I should head next. As always, refer to '1' - personal objective for what you want to get out of the game.
My usual playthroughs, for approximate zone order: First half of Hinterlands, Fallow Mire, Storm Coast, Haven main quest (In your heart shall burn) to get fortress, second half of Hinterlands, Crestwood, Western Approach, Adamant, Exalted plains, Wicked Hearts (main quest), Emerald Graves, Arbor Wilds main quest, Emprise du Lion, Hissing Wastes. For that particular order it's more based on character level, plus doing the Plains before the Graves adds a little extra dialogue in regards to a hostile group encountered in both areas when questing in the Graves. Anything else is whenever I feel like doing.
I know that wasn't fully compressed but I only know how I enjoy playing the game, not how your buddy does. Best way for him to enjoy it more is for him to decide what he wants to get out of the game. I personally explore everywhere and try to do every quest, find all the codex entries for lore etc.
I have Asperger's Syndrome so understand what it's like to suddenly get really interested in something, I hope your buddy continues to enjoy the game 