Heres the cheat code: follow dress code at work. If they have a uniform, wear it properly. If they allow for casual clothing, go above and beyond and dress to impress. I'm not saying to go broke on clothes, but wearing a button up or a blouse over a printed tee gives a better impression
Be punctual and, no matter the circumstances, be kind and courteous. Even if you're being screamed at or just having an overall bad day, always be kind to others.
That's it. People will think you have your shit together when you're actually pretending. I've gone to work en emotional mess and barely keeping it together, but I never let anyone know and I've got a lot of compliments on my maturity
But it's all an act. I'm a borderline retard in my free time

Because they're making a huge profit from it

Former McDonald's employee here, I agree with unklethan