What do I need to remember before starting a new playthrough of DAI

Maybe bit late, but:

a) Play with character creation. It is big enough to spend some time here and you have a lot of time-screen with your character (adding this one since friendo always go with one of the default faces and then makes big eyes how beautiful or cute characters someone makes). And if you forget about something (for example, I started to play again and my Inquisitor looked as if she met with shovel few times too much) there is always mirror in Black Emporium (if you have it installed)
When you get to specializations always go to tactic screen and put the special skill on use. I didn't do it and wondered why my companions run around with maxed focus (focus? me sorry, me no native english speaker)
c) If you have enough of your class and want change BUT you are in middle of gameplay, simply play during fights as one of your companions. I found mages really OP with their range for spells (don't judge me, since I play I've been always rogue only) and I couldn't help myself but play as mage this time. It hurts tho with opening rooms in Haven (under it) and I cry inside. But I'll be stronk!
d) As SofaJockey wrote, leave Hinterlands if you have enough of it. What you need from there from beginning is simply go down, kill few people and talk with Mother Giselle. All
e) Check them links people posted above me. I found them during my gameplay already when I reached Skyhold and with few I facepalmed a lot that I missed things
f) Read perks you can get and think about them. If you want to collect everything, from Secret tree reach perk with opening locks. BUT when you gain Agents they count as well so no need to spend your perk on something you aren't happy with
g) I think it's somewhere in the text from link, you can't re-take your perks. Word of advice from me - take all perks with knowledge. Since there is one mage in Hinterlands, I would recommend Secret kownledge perk about magic. Useful, for me
h) If you want some nice talk between your chars, don't make same mistake like me and don't wonder around with only Cass, Varric and Solas >.< I found about it already when exploring Hissing Wastes and again got bruises on my face for my stupidity. There are a lot of talks between all of the chars.

i) Enjoy, play as you want, and... ask people here. I believe everyone will like to answer you or give you some advices. If you want to have from Inq as much as you want, don't rush, go explore! \o/ I've spend over 260 hours and still didn't found one special shield or original chainmal armor

And, at the end, word of advice from my playing:
j) Explore. 0_0 There is so much hidden. Look at the rocks, at the paintings, buildings, read codex entries...
k) It is not really necessary to always have warrior, rogue and mage in team but it would be wise to always go with that team-comp. There are missions where you need only rogue and can take whoever you want (but I do recommend warrior as he is tanking everything *bows to Cass*), there are a lot of Veilfires which requires only mages (so it should be, always take mage). I remember my *disguised noise* when I went on bottom of dungeon and there was wall to break only for warrior. Guess what, climbing on top, going to camp, then long way back to dungeon on bottom and crashing the wall for two chests with... nothing important/stupid stuff to sell only
l) Simply enjoy. And use F5 a lot.