I would say reasonable notice helps a lot. I actively enjoy spending time with my family so I regularly talk to my parents and invite myself over/get us invited over when I know we're both free (with BF's agreement). Similarly, I know that there are certain weekends of the year (birthdays etc.) when we are likely to get together and plan my mental calendar accordingly. I let BF know about this and there aren't any surprises.
BF's family are lovely and welcoming - but frankly, they're just not as much fun (to me) as my own family. His father is absolutely lovely, but mother can be a bit possessive and seems to delight in disagreeing with every vaguely subjective opinion I have, and his brother is overly competitive. So while they are nice.. they're just not as much fun to be around as my own family (3 of us kids and lots of lively banter). That said, I do know they like having us around (and it's not fair on BF for me to want to spend all family time with my own family), and I do regularly suggest to BF that he ring them and invite ourselves over/suggest dinner etc. That's all fine, and when we have a free evening, it's nice to see them.
Unfortunately that doesn't appear to be enough for his mother, who has been known to turn up at our door to drop something (totally unasked for) off, and announce 'so we're seeing you at supper this evening then.' If we do have concrete other plans, then it's easy enough to say so, but if we had vague plans that involved just the two of us, I hate being put on the spot - as does BF. BF however isn't very good at saying what he wants to do, so I end up being the one to say no/not sure, and getting the stinkeye from his mother. It would make life so much easier if they just rang him up, said 'we'd love to see you x time to do y', but you talk to jammytoast about it and let us know whether you can make it'. That way we can discuss it, and get back to them without any pressure/guilt tripping.