How do I teach my 3 year old proper "We have company" etiquette?

Although most people expect that and are ok with it from a 3 year old, I would probably encourage independent play often, not just when people are over just in general so she can start to enjoy her own company, maybe bring out a special toy something she doesn't play with everyday when you know your having company, to keep her interest a bit more, also when she starts to in your words pester people try redirecting her, your probably doing all these things but that's what comes to mind for me......

Sweetie, she is the center of your world. You and SO drop everything for her. Why wouldn't she expect the same of everyone else? Especially when enough people have shown her that if she does (insert behavior) they will read books etc.

What worked for me, "we are having company". overload her on mommy and daddy time ahead of time while letting her know once the company is there she has to do a quiet activity. A movie, coloring books, toys.

I would maybe stop my interaction with the adults for 10-15 mins so they didn't feel too lonely but let them know I will be here for a bit then I am going back to my playmates...

What? You mean they don't all come over for the sole purpose of visiting her? The horror!

I think she's old enough to start really learning that sometimes she has to wait before getting attention. Like when you are on the phone or taking to DH (or just busy) and she wants your attention RIGHT NOW, calmly explain how you would love to talk/play with her after you finish this conversation. And I give him the same chances back - when he's busy playing, I'll ask if he can come brush his teeth (or whatever) when he's done building that lego tower.

Can she count well enough to kind of use a digital clock yet? Like I'll say at "See the clock? When it turns 4:30, I'll come play with you" or "I want to talk to daddy for 10 more minutes, then I'll talk with you. That will be at 11:35" It gives him something concrete since "later" is such a hard concept to deal with. We use the clock a lot with my 3 year old to help him be patient for attention or food or to anticipate transitions. He loves numbers so this works for him.

And I know this will take a while to really sink in, but I'm also talking to my 3 year old about "polite" vs. "not nice" behavior, and about how things we do can make people feel different things. He cares a lot about having people be happy and obviously he likes to be happy, so we're currently having a lot of conversations about feelings and how being nice and polite can help people be happy (or other behavior can make people scared, sad, angry, frustrated, etc.)

And then I tie all that with lessons on patience. It's still obviously tricky for him to understand it all, but I'm starting to see some progress. Hopefully this might help in your house too.