Tips for interacting with service workers

Hi,

As I study Japanese, I've become increasingly aware of the importance of hierarchy! Furthermore, I'll be vacationing in Japan and anticipate my most common interactions with be with service workers (e.g. wait staff, cashiers, hotel staff).

Thus, I was wondering how I can most respectfully interact with Japanese service workers, while respecting the social hierarchy!

Should I use formal language, or just keigo with colloquialisms? Is it okay to refer to them as お兄さん or お姉さん¹, or is that too casual²? Are there any other unspoken rules/advice I wouldn't even think to ask about?

Thanks!

¹A brief tangent, but is お姉ちゃん preferred over お姉さん or is it too diminutizing/condescending?

²btw I'm probably younger than or the same age as most of them, in case relative age matters