For anyone jumping in as this hits Game Pass, I wrote up a few tips that will hopefully help. The game really isn't that complicated, but it does little to tell you things, and there's a few weird things you wouldn't think.
D4 getting started:
-Remap your controller right away. By default, primary attack and interact/pick up is the same button. One of the sticks doesn't really get used by default. The default makes it impossible to pick up things. Controller works pretty well once you get the hang of it.
-Go into the gameplay settings and enable both advanced tooltip options (let's you see better stats on items)
-In order to level up the battle pass, you have to play a seasonal character. Don't buy the BP unless you plan on playing a new character (seasons are a great way to try a new class). We're late in this season, so I'd probably hold off until season 4. You can skip seasons and just play eternal realm, but again, no battle pass leveling. You have to be seasonal to do it (which isn't great). The pass is nothing special, but usually has one good gear set. The microtransactions otherwise are comically overpriced.
-When you start to get legendary gear (orange), keep it all for now (either use it or put it in your stash). Gear has aspects on it which come in handy later on. This is getting a major rework in May, but for now, some aspects get stored in a codex, others take up space in inventory (it is confusing as ****). Just stash them for now. Even if the gear itself is lower level, the aspect might be useful.
-The community is fairly toxic. The very endgame is a little weak in this game. Season 4 and eventually the DLC should help. Most of the Youtubers are fairly awful. Just don't be surprised to see people super angry. Just tune them out, game is fun.
-Dying (unless you play hardcore) has little penalty. You just have to go to a blacksmith and repair your gear after you die (don't forget though as it is easy to not realize).
-To start, get the campaign done. You can jump on side quests anytime (blue !), but they never go away. Unlock a fast travel point anytime you are near one. There's things called Altars of Lilith that you need to find and interact with. That unlocks renown, which is something you'll want to do if you plan to play past the campaign.
-At the start, just pick the highest armor or dps number on gear early on, don't worry about stats until you get past level 50.
-It is recommended you follow a build guide, even early on. You can just pick things, but chances are, you'll eventually hit a wall. maxroll.gg has a lot of great leveling guides. Leveling guides are useful into world tier 3, then you switch to endgame. You can respec without much fuss though (just a little gold), so don't sweat anything, especially early.
-Don't worry about gold. Salvage any junk you find.
-After the campaign, the goal is to get to WT3 and eventually 4. A little before level 50, switch to World Tier 2. Then at 50, you can complete the capstone dungeon which unlocks WT3 (then another one at 70 for WT4). These are tough things to get past and will test your build. If you aren't doing great at WT2, you probably need to adjust your build. You can push these things earlier, but it is only recommended for experienced players. If you are playing early and it is too easy, bump up to WT2. You can always switch back.
-World Tier 3 is sort of "endgame tutorial". All the concepts are the same, but once you get to WT4, you'll dump your WT3 gear pretty quickly.
-Again, you'll figure out things as you go. From 1-50 or so, just have fun.
-Hack, then slash. Always. Never the other way around.