It's hard to say really. For example, though I do believe people can change, don't try to make your loved ones into someone they're not. Sometimes people expect you to be different than you are (not in the easily changeable ways, but by nature or deepy ingrained habits/beliefs).
We just have to be open, honest, and okay with really accepting someone for who they are, and not just who they could (or we want them to) be.
Apart from that, I'm sure their are a few more. Like how some women almost expect a guy to be like another woman. Seriously, we're not supposed to be. We're Men.
On that note, some girls think they want prince charming, but call many of the acts/principles of chivalry, chauvinism. You can't literally have both. Either be okay with a guy treating you somewhat in the typical 'woman' model, or don't. Many things in life aren't customizable, lol.
I'll try to think of some more, but that's a start anyway. I think the typical 'be great looking, successful, sensitive, good at everything, and perfect' expectations everyone has are obviously unrealistic. The same goes for the intense romanticism that oversweeps our country. There are just a lot of lofty expectations sometimes....