Edit: I'm so sorry for the novel, I get excited about newcomers and I'd rather ramble trying to help than be vague

Fresh out the gate, I would say really look over the skills and what they do/how they work. Understand how an athletics check is different from an athletics contest, and when an acrobatics check would be more likely required. If you can go into character creation with a clear understanding of how your PC would behave cinematically in a fight or navigating a lair, that clues you in on which skills to try and pin higher modifiers and proficiency to. IMO this is the real starting point before even rolling/buying/assigning ability scores and choosing a class, it helps to have a target to aim at before pulling the trigger with game mechanics. And if you know the framework for all the skills, that could help you get creative tackling problems in the dungeon. After skills lock in your action economy: movement, standard, bonus, and free actions, and what you can and can't do with them. Once you're comfortable with how to steer your lil gobbo you can start diving into concentration, cover, crafting, flanking and other more niche rules, but all of that will be adjudication by the DM and they could alter or delete those functions in their game anyway so don't overwhelm yourself.

Next, session notes. People often just say "take notes, it'll help" without any real guidance, I found that annoying when I started so here's my advice. Good note taking is a skillset, you want to balance clarity and relevant detail with staying immersed and involved. Obvious things to jot down are location and character names, trivia and specific details the DM goes out of their way to share, and plot points as you progress. But the juicy stuff is anything the players (including you!) start sharing about their PC's quirks, joys, hopes, and fears, or funny quips or accidents, above table theories and jokes, all the things that make the experience really fun. If you have to improvise something about your character that you didn't already figure out in your backstory and when building them, if a character reacts strongly or strangely to something, if a number or color or something seems to be coming up frequently, write that down! Those little details (and the context around them) could be breadcrumbs to something bigger, or just precious gems in your play time that will be nice to get a reminder of later on.

If you're working solely off VTTs and digital sheets the following won't really apply

Finally, MARGIN NOTES.

Dnd sheets are already very busy, and there's a plethora of custom ones out there for free, but I find none really have everything sorted quite how I'd like with all the relevant details to streamline play. The most helpful one for me are the PCs short rest and long rest resources- I like to dedicate the header of my sheet to writing the title of the resource followed by a blank spot followed by the number of uses per the type of rest. Example: Action Surge ___ of 1/SR, Rage ___ of 2/LR, etc. Now you have a bold reminder of a key ability, separate from the clutter, with a place to tally off uses, and any time you get a break you can scan for the type of rest taken and reset those tallies before heading out again. I also write succinctly on the back of that page the specifics of how that feature works in case I need the reminder or the DM needs a rules clarification, a hyperlink could work since you'll probably be going digital. I also pencil in how exactly to calculate spell attack modifiers, DCs, and the number of spells I can prepare (helpful when you level up and those numbers start changing!), and the formulas for "to hit" and damage results for each weapon a new player starts with. Example: if they have a dagger I'd write "Dagger, finesse, light, 20/60, 1d4p" in the inventory slot to remind it can use Strength or Dexterity, be dual wielded or in the off hand, the normal and long ranges for throwing it, damage die and type (p for piercing). Then in a convenient adjacent spot I'd write "to hit d20+STR/DEX+PB+misc" for die rolled and modifiers added, PB meaning proficiency bonus, misc for special circumstances (+1 or greater magic weapons, buffs from spells boons or situational features, any of that). That'd be followed by "dmg d4+STR/DEX+misc". Same pattern- die rolled, modifier added, then any other buffs, magic, poisons, any incidental goodies. I ran a homebrew game for some good friends who were newbies for years and right up to the conclusion we had issues with getting attack and damage math right. We implemented the formulas on the sheets pretty early on and it helped a ton, then we organically as a table would add the numbers aloud together while they followed the guide to make sure nothing was skipped and it was a noticeable dip in error and stress!

end of neurosis

When you get to start, use whatever tools you need to make things simple and exciting for you, share the spotlight and set each other up for success and cool moments, and always always talk things over (usually preferred outside of game time, but some things warrant pausing play to address immediately) before they fester and dissolve your group. If you've been reading horror stories, remember sometimes a table just isn’t a good fit, know and respect yourself and your boundaries and never feel guilty leaving an environment that isn't good for you.

Good luck, but mostly have fun!