I've found that the most effective way of managing expectations, at least for me, is to expect people to be themselves. Sometimes it might take a little while to establish whether someone's reliable or not, and that can be observed by the way they treat people generally - not just me.
I have enough friends who I know ARE reliable, and if they've said they'll do something then they'll do it - or if there's a problem, will let me know immediately. I quietly drop anyone who doesn't, or who lets me down repeatedly - or manage it in some other way. I had a 'friend' years ago, who I wouldn't arrange to meet up with unless it was in an environment where I'd be happy to be on my own, because she would likely not turn up. In the end, I got so fed up with her I just stopped returning her phone calls - but I know I wasn't alone in that.
On the other hand, the only realistic expectation we can have of a drinking alcoholic is that they will drink. The detachment I've learned in Alanon has been very helpful in standing back and asking myself what I can reasonably expect of another person - not people in general, but any one person in particular.