Looking for general wisdom on appropriate way to manage relationships with boss and clients

Hi folks,

I wasn't sure where to post this.. so I figured I'd put it here since I'm looking for advice from any professionals, really.
So I got my first ever role as a data/IT consultant at a boutique place, hooray.
Now the problem is I got extremely lucky landing this role and I'm coming in with mainly a science research background... meaning I don't think I should translate the way I approached my relationship with professors and lab managers (very casual) to how I'll be approaching the people in upper management. Or at least I don't intend to, I'd like to keep things as professional as possible as I enter my first role.

I came from a working lower-middle class background and my parents are blue collar workers -- so no one in my family really knows how to advise me on appropriate conduct with clients or upper management in this sort of professional setting. Hence I am turning to WSO for some advice.

Now the root of my confusion comes from my exposure to people telling me that I should try to be casual and friendly, be myself, blah blah, etc. And then there's the other school of thought who has told me over the years to keep it as formal and professional as possible. I'm not really sure how to reconcile these two pieces of advice in a way that's appropriate; I don't want the people I interact with to experience a tonal whiplash that I know I'll end up causing somehow, someway if I'm left to my own devices.

So I'm here to ask how I should approach my work relationships with the people I work with? I'd ideally like for the people I know to understand that I'm a friendly person... I am grateful that I was able to get a job so I want to be able to present myself as best as I can. I'm a sociable and amusing person too, so I want to be able to convey that to the people I work with and the clients I'll have to be interacting with.

I'd like to ask the professionals here on WSO on general workplace wisdom when it comes to interacting with clients and the people who manage you. What is and isn't appropriate (and I mean the subtler things to keep in mind... not the obvious "don't talk politics, don't talk about dirty stuff, etc")? When should I usually be keeping it 100% formal and when should I be able to relax a little bit?

Sorry if I sound really dumb asking this... I figured I'd at least ask and get some advice to start planning now instead of reinventing the wheel.

Any genuine help is appreciated, thanks!