First come, first served
The way I arrange my schedule is, first come first served.
Meaning, if I had arranged for an appointment on, say, Saturday night, with Bunch A friends last week. Then Bunch B friends call this week and wish to arrange to meet up on the same Saturday as Bunch A friends. I would naturally tell Bunch B friends that I’m sorry I can’t make it because I’ve made a prior appointment.
People shouldn’t expect me to drop my prior appointment for them if it isn’t an emergency. Same goes for family appointments. As in, if I’d already made prior plans with friends, then my family shouldn’t expect me to cancel my appointment with my friends just because, well, they are my family. Of course, there will always be exceptions e.g. if it is an emergency or an important event (like a wedding or birthday – but then these should already be known in advance and planned accordingly.)
Why? Because I think it is rude and inconsiderate to cancel on people at the last minute without concrete reason. Would you (family or friend) like to be stood up at the last minute? Similar to informing people of an event at the last minute. Which is why I try to avoid doing things like these as much as I can.
I’d just recently had some friends back out on a meet-up that’s been arranged a few weeks in advance and postponed a few times, all because of work. Which is a lame excuse, if you ask me. If it were an emergency, then fine. Once or twice, it’s ok. But multiple times? Ugh.
Obviously, if I could accommodate all parties, I would gladly do so. Unfortunately, sometimes it’s not possible to split myself into pieces to be multiple places at one time.
I shall let my family and friends tell you about me. These comments may be rather old but I think the gist of them still hold 
