If you're not able to just say no to these things (and I know some people struggle, I used to suffer terribly with social anxiety) then the thing you must always remember is Do Not Commit! That's the mistake people make!
I know it's hard - colleagues are chatting enthusiastically, making plans, "Oh you'll come won't you Lee, you have to come" and you feel like a rabbit in the headlights so hear yourself saying "Oh yes, sounds GREAT". Then you're thinking Gah, WTF?.
If this is you then you must learn the skill of Not Commiting. You can make enthusiastic noises if you feel you must but remember your mum was going on about that family celebration dinner? It's either that weekend or the next, you won't know til selfish bloody SIL
stops with her drama so you're not sure yet. Or maybe that's the month MIL is expecting to have a (little, nothing too serious) procedure and she'll need looking after. No date yet grrr, bloody NHS, poor MIL etc
. So unfortunately you're not sure yet. And so on and so on cos once you start with this stuff you'll be amazed how easily the lies trip off your tongue. Then after a couple of days or a week, when the big group plan is set in stone, you can do the "Oh it's so unfortunate, what are the chances, ah well you all enjoy yourselves" thing and you're home free
.
If you can say no but need a good excuse then you're more than halfway there. There's the examples above (with firm dates), there's your sibling/cousin/friend who'll only be home from foreign parts that weekend, there's the clash with your sisters anniversary night out, her dc are having a sleepover at yours don't forget, there's DHs best friends 40th... Oh it's such a shame, otherwise you'd have loved to!
These days I'm well able to politely decline these things just because I don't want to go but sometimes you really do need an excuse and in those circumstances it's always good to have a selection of lies escape options in your repertoire.