One thing that isn't spoken about enough is that being an engineer at a startup is it's own unique discipline - it's almost completely unrelated to the kind of role you'd have in a company like Google or Meta. Before you accept a role at a seed or series A startup, it's worth knowing what you are in for and what it takes to really excell at it. Having been round this particular merry-go-round more times than is healthy, I thought I'd write a few notes which you might find useful:
Options > Salary
When it comes to rewards, make no mistake - you are here for the stock options (and the learning). Startups are extremely constrained by their cash burn so you'll struggle to get an amazing salary BUT what startups have a lot of is stock in the company. It's not uncommon for seed stage companies to be giving you well north of 1% of the company's equity in stock options. It's a big risk but if you believe in this company then you can walk away with a life changing amount of money. Negotiate hard on the options - it's good for you and the founders - you're all motivated to make this thing work.
Know the product and customers
It's blindingly obvious but the lifeblood of a startup is it's product and customers. It's so tempting, as an engineer, to get wrapped up in some sidequest (choosing the best framework, putting together a state of the art data pipeline etc etc). Get to know the product in detail, get to know your customers - spend time doing support, dig into the data, look at competitors, become a customer! - find a way to become obsessed with the product and if you really can't then consider finding another company.
You're the expert now - Act like it
One thing I've seen a lot is engineers joining startups having a huge crisis of confidence. You need to realise that this whole company is a group of people who are winging it for most of the things that they are doing - chances are they hired you because you know more than them about a lot of things so don't wait for reassurance and sign offs - just roll your sleeves up and and start shipping stuff.
Be scrappy, really really scrappy
A successful startup is constantly doing things that don't scale. Don't get caught up building some amazing architecture that encompasses all kinds of invented future possibilities. Fixate on what the company needs you to do to get to the next step and just work on that. Don't introduce any tools or processes unless they are solving a present problem. Don't solve problems you don't have. Put out the fire, then move onto the next thing.
Be a jack of all trades - but prioritise
You might be surprised to find that you might spend a large proportion of your time at a startup doing things that are not in your job description. If you are a front end engineer, you'll be writing back end code, but you might also end up being the adhoc network engineer or jumping in on customer support or organising the holiday party or collecting the milk or ... well, anything. Always protect your own time and energy so that you are working on the highest impact thing you can but sometimes that high impact acitivity will not be writiing code - go with it. Don't be a afraid to wing it, just get involved. On top of that, you'll learn a ton.
You are all in it together
When you join a startup, think of it as becoming one of the founders - you all own part of this company after all. The really exciting thing about this is that you can be a part of shaping everything about this company from the product to the culture and everything in between. Own the whole thing - if something is broken, don't wait for someone else to fix it or get all blamey - gather a crew and figure it out. The thing that always amazed me is, even in a huge company like Meta, the imprint of the early employees is still there - fundamental ways of working and thinking haven't just come from Zuck and the leadership.
I got a huge amount out of being part of startups, it's taught me enormous amounts, it's introduced me to amazing people and it's given me the opportunity to achieve some things I'm truely proud of. However, it's not for everyone. It's definitely going to hurt - stress, overwork, fear and uncertainty are all a thing. Hopefully, now you have an idea of what it takes to do it well and can dive in and make the most of it if you decide to take the plunge.