This is something I'm still learning myself, after 7 months in the ER.
The short answer: prioritize, prioritize, prioritize. You're constantly sifting through "the list" of things to be done and figuring out which is your most pressing priority. All of your patients breathing? Check. Who is your sickest patient? They're next. Who needs something completed so as not to delay further care? Next. And so on ...
The family, doctor & patient may all
want your attention right now, but it's up to you to figure out who/what
needs to be addressed first/next.
Good luck to you - hope you find your experience in the ER as rewarding as I have.