For the most part, I consistently screwed up when I started new work. 
Being a nerd usually means no instinct for social norms or conventions, and it took me more than 25 years to catch on to what humans normally intuit.
Here's my brief take on what I wished I'd done, and some of it will sound cynical.
Once you're in the company, figure out whether the culture is about building a good product, or about telling a good story and looking good.
Sun Microsystems built great Unix-style servers and dominated much of the growth of the Internet. However, they never told a good story about themselves, and failed.
At IBM I tried pushing Unix systems, failed, and failed again.
Marketing (telling a great story) is mission critical, but if that culture dominates your culture, you have a problem. Climbing the corporate ladder might become more a matter of looking good and exuding confidence, which is labor-intensive.
People who get great at telling a story might never learn to build great products, and worse, might never respect what it takes to build stuff.
So, your first task after getting inside might be to determine if the boss is an "empty suit," looking good and projecting confidence and that's it.
Then, you decide if the culture is a fit for you.
To be clear, the ability to tell a good story is mission critical, and not just for company product. It applies to you as an individual.
From the very beginning, take responsibility for your image, how people perceive you, your brand. The idea of a personal brand has become devalued, but it's a real thing. It's about how people will decide if they want to work with you.
Your effectiveness will be amplified, or reduced, in this manner. Our species is collaborative, and usually gets stuff done within networks. Without that, we'd be extinct.
I've never been good at telling a story, which is reflected in this piece.
Don't be like me; for example, realize that being right often doesn't matter, and confrontation is frequently counterproductive.
Some things matter, some don't. Figure out what fights are worth fighting, and which aren't. People prefer to go with the flow, to collaborate, or at least to avoid trouble.
There's a lot more to be discussed, like the value of ***authentic networking***.
However, no one seems to talk about this big-deal difference between corporate cultures, and how much it determines your happiness at work.
First thing, figure out what that culture is about, and maybe if you don't like what it's about, plan a future which involves finding a different place to work.
