I know a lot of meta because I personally know the DM.

Just FYI, a lot of us know our DMs but don't get told anything. That's probably how it should be in your case.

Now if you want to request something happen to help you become an Arcane Trickster, that's fine. But the DM's response should just be "OK." Not "Here's the whole plot that will result in the thing you want."

You are thinking like a DM here. While world lore can fall under the purview of players (and I love when my players do it), I don't think that privilege is helping you right now. You need to give up your desire to design the campaign world and history and just focus on your character's basic motivations and traits so that when the DM tells you what the world is like and what is happening, you can react through that character.

Meanwhile, go ahead and write pages of yuan-ti lore if that's what you enjoy. Maybe you can use it in your own campaign later on. You don't need to have a character 100% fleshed out before you've started playing. You tie it into the world by reacting to that world as you play. So put down a few bullet points about your guy and then go write about his uncle or something with the understanding that its your own spinoff story and not canon to the campaign your character will be playing in.

You might think that you are helping your DM by creating all this lore. Because that's what you're good at, right? Well, you're probably not helping. Trust her to make the world. It's her campaign to run.

Just FYI, a lot of us know our DMs but don't get told anything. That's probably how it should be in your case.

Yes.

I would consider the stuff your DM is telling you to be spoilers and I would ask her not to tell them to me.

Note, I support being as helpful as possible to the DM. For example, one thing the DM can struggle with is "why are these characters going out on adventures?" Lots of players, especially newer ones, write backgrounds that make it hard to picture why their characters are going on adventures. They all seem to want to make a Bilbo Baggins who struggles against going out into the world. One character like that is maybe OK, but a whole party of them is not.

To help my DM, before he wasn't able to do it anymore and I took over, I made up a Bard whose primary ambition is to write the next great heroic epic along the lines of Gilgamesh or Beowulf. Thus she wants to follow "brave adventurers" around and chronicle their exploits. Which means, of course, every time they have a choice to make, she'd push them into making the brave, risky, heroic choice, so she could write a stanza about it for her epic later. The key reason for doing this was to have a good, IC reason, for my character to push the party to do each and every possible quest they might run across. I did this because I thought it would be fun, yes, but also because I thought it would help the DM to have one player whose character is always ready to take any plot hook he dangles in front of us, and run with it. It makes his job easier. Just tell my character there is a town being plagued by orcs, and she'll do whatever work is needed to get the party to intervene. 

But, I did not ask to know plot points or any of that. My way of helping was to make a character who would go along with the DM's general plans, not to know what those plans were.

However... every DM does it his or her own way. If telling them plots ahead of time is making it more fun, then that's what matters.

I find just answering some simple bullet points is enough for creating a character. And leaving background details vague until later is fine too.

As a DM I look for

• Mechanically, what role you want to fill (weapons vs spells, ranged vs melee, super skilled, party face, etc)
• why you adventure
• do you have any enemies or allies that may show up later
• some basic personality traits
• And then how do you feel about some setting specific stuff

A lot of the times for ideas, I will see a subclass I really like the theme of, and then go from there.

A recent example: in the Wildemount book, I really like the Echo Knight fighter. And I have wanted play a bugbear for a while, since in another game I was in, someone else's bugbear was very memorable (dumb as a box of rocks). And looking at the backgrounds, I saw the Volstrucker Agent, and it caught my eye. I ended up with:

Wurt, the bugbear echo knight fighter, who thinks that his echo is actually his invisible friend Eric. Sometime in his past, he accidentally got caught up with the Volstrucker network, which is probably how he also got his echo knight powers. But whenever they send him an assignment, he thinks its just Eric writing to him. Just it happens to be to go murder something or break their kneecaps. He is otherwise very good natured.

For the game my DM is trying to run this is enough. The specifics of what the event was in his past don't matter, or if they do later, we will just come up with something then.

• Frontline fighter
• He adventures because his invisible friend tells him it would be fun to go places.
• The volstrucker network is a manipulative ally of his
• He is very trusting (too much so)

If you give your DM just a few hooks to play with, they can usually figure out a way to hook your backstory in. I wouldn't worry too much about writing yourself into the world before you start playing, that is what the campaign is for. Everything after showing the girl the tile looks like you are writing what is going to happen, but that is ultimately for the DM to control and I wouldn't focus on it.

From what you wrote, I have:

• From a sketchy Yuan-Ti family
• Got sent away for something (digging too deep into something / fill in the blank if it matters)
• works hard, seems reasonably personable, and a little too curious
• adventures to gain the knowledge / power they need to return to their family / to be accepted by their family again.

As a DM, great, I have some NPCs to play with: your character's family, anyone your family has pissed off, and some adventure hooks: lore about your family.

Wow I can't tell you how much fun I think it would be to RP with someone (or GM for someone) whose character has invisible friends. That just sounds like a blast.

By the sounds of it you are starting with the backstory before having a character sheet created. I have a similar problem myself when developing characters. I think the easiest way to get around this is to fill out your character sheet before writing down anything else.

I really like this site (http://pathguy.com/ddnext.html) for my basic character creation. I would and have used D&D beyond, but because I prefer to have my books "in hand" and don't feel the need to buy them twice. So I use sites like this instead where the basics are incorporated without being overly flashy.

And the nice thing is that the character personality and backstory are placed at the bottom of the page where you can spend as much time as you want because everything else is already filled in.

When I'm creating a character, I focus on three things, in no particular order:

1. What would be interesting to see in the premise the DM has proposed?
2. What is an interesting class/race combination?
3. What is a class or race that I haven't played before?
4. BONUS: is there a point of inspiration that I got from elsewhere that I'd like to play with?

Here's an example of a character I whipped up for a campaign my DM is thinking about running next year. I was able to whip her up in an evening.

Premise is a Blood Wars-themed campaign where the Abyss won and the Material Plane is being overrun by demons. I review the list of playable races and think, oh! An aasimar would work perfectly for this premise. It makes perfect sense that a good-aligned deity would want to send a scion or avatar to the material plane to fight the demon scourge. (As a bonus, I haven't played an aasimar in 5E yet.) Speaking of, the Scourge subtype is intriguing to me, so I pick that. For a class, I figure that the Barbarian abilities would synch well with the Scourge aasimar's racial ability, and I like the idea of a "wrath of God" type figure instead of your typical more placid cleric. The Zealot subclass thematically fits this, as well. (As another bonus, I haven't played a barbarian before.) Finally, in terms of personality, I like how Griffin McElroy in TAZ plays a barbarian who is generally foppish and dislikes violent confrontation - lets turn that up to 11 and say this aasimar was raised by humans who follow a pacifist religion, kinda like Jainism. Now we have an interesting character conflict! The values that she was raised with conflict with her inherent nature; maybe she is afraid of going into a rage and avoids it as much as possible.

Badda-bing, badda-boom. I have an interesting and coherent character concept ready to go. I don't know every single detail of her backstory yet, but I don't need to; I already have enough to work with. The rest will come out once I start playing her.