In one of my first professional experiences, I did everything you should not do at the start. I showed up late to the office, I left too early, I forgot to attach documents to my emails, I had no idea how to approach people in the company and learn their stories. I asked questions whose answers I should have known, and I failed to ask the right questions where it mattered. I was professionally unpolished material, and it showed.
Looking back (besides wanting to give myself a retrospective smack on the back of the head), I do forgive myself, though, unfortunately, especially when I realize that many of the rules understood by experienced people are unwritten, left for you to discover the hard way. So that you do not end up with regrets too, here are a few of the things I learned.
If you have not figured out the culture of the company you are part of, grab a pen and a notebook and investigate as fast as possible.
Every company (whether it is a startup, a multinational, or anywhere in between) has its own culture. In some companies, the principle of "radical candor" is the norm, where people give and receive feedback constantly, as directly and as honestly as possible (however hard it may be to swallow). In others, you have to be careful to wrap your language in polite subtleties. Here you can message the CEO anytime; there it is a sign of disrespect to bother a senior person with your trivial problems. In some places, you will have clearly defined responsibilities; in others, you will have to figure out for yourself what to do and how to do it.
Diversity in professional cultures is normal, characteristic of any group of people who have something in common, something that simultaneously sets them apart from the rest of society. The thing is, if you want to stay in that place, the language specific to it has to be perfectly clear to you.
You do not move to France without learning French, so do not expect to flourish in a company whose language you do not know.
You will not know, so you have to get used to learning.
At my first job, I expected it to be easy. In my mind, if they hired me, it means (by reverse induction) that I already know what I have to do, that I have all the necessary qualifications. The thing is, every company essentially does something different (otherwise it would not stand out in the market). It sells a different product, in a unique way, has its own metrics and a whole series of other particular traits. No matter how talented you are, there is no way for you to know all these things at the start. More than anything, you have to develop your appetite for learning, to understand that you have an informational mountain to climb, and not to get demoralized when you do not know what to do right away.
Ask the questions.
It is slightly terrifying to ask questions (especially if you are just starting out) (and if you are in a meeting with the whole company). It seems like you did not do your homework well, like you are admitting your ignorance, and if the question is not phrased well, you also risk making a fool of yourself. The thing is, the only way you can learn is to get past this initial threshold and start asking left and right about the things you do not understand.
One of the smartest people I know (a genius, in fact) was my classmate in the first year of philosophy. This man kept his hand up almost all the time. And if he did not understand a basic concept, he would ask five times until the concept became clear in his mind. At first, I kept wondering how he was not embarrassed, how he had so much confidence to keep asking. Until I realized that the ultimate reward, of fully understanding and internalizing every concept all the way through, is so appealing that it is worth getting past your inhibitions.