I mostly learned from watching Trump videos on youtube and watching him stream while at work. For all the RNG in the game, your actual draft is still slightly less important than your skill in playing, but obviously the draft IS important. Trump can get to like 8-9 wins with some seriously stupid decks. I'm 8-2 right now with what I thought was an awful Paladin deck.
So when drafting, the curve is pretty important. You want 2 drops, 3 drops, and 4 drops. Ideally you want some strong endgame. You want cards that are good at going 2-for-1 or otherwise eating up removal resources (Harvest Golem, Yeti, Scarlet Crusader). You want overall strong cards. Don't bank on getting combos, unless you pick Hunter, then you may as well go for it. Mage is overall the most reliable but I honestly have best luck with Paladin. I believe Druid and Shaman are also strong picks if you're just going for the in flavor.
Trumps arena rankings are a good baseline to start with too. I used them religiously when I started arena but since arena is really all I do, I've gotten to the point where I use my own judgement now. Anything in his top 10 neutrals though you should usually pick 100% of the time, those are just strong ass cards.