Use the Inquisition perks. Important perks to unlock as soon as they are available:
- Deft hands
- The 3 perks that unlocks more dialogue options
- Extra potions
- Extra inventory slots
Gather everything, all herbs, metals, crafting materials etc. Purple weapons/armour are not that great, you will get better stuff almost always by crafting. Don't stay in Hinterlands for too long, move on to Storm Coast, Fallow Mire, Crestwood when you have sufficient power to unlock these areas. Do not sell all valuables before turning in items for Creature Research. They give you important stats and will be lost if you just press Sell All. This is a Bioware RPG, so talk to everyone. Talk to all companions whenever you return to Haven. Save often, usually before conversations, incase you get a huge disapproval rating and need to reload.