I write it down on my phone calendar and set an alarm for the night before.
Kids go to after school club on days I work, DH collects then. Days I don't work I aim to get to school at least 5 minutes before the bell. The time I leave is a hard deadline.
Some mums on the WhatsApp group post reminders for things, they are helpful!
If it's inset days or half days then either DH or I take leave or if we are working from home the kids are old enough to watch the iPad without much intervention.
School holidays are paid childcare, mix of me and DH taking leave and my parents having the kids for 3 days. We scrape our leave and build up flexi to cover.
I don't really rely on other parents. I've taken friends kids on half days or inset days or for full day playdates to help them out.
On the flipside I'm absolute shite at organising playdates for my kids and worry they are missing out. I'm shy and not good at asking folk for that sort of thing so I may have my shit together for the school stuff, i need to sort it out for the social stuff.
Basically, just get your shit together. Use your phone calender and set alarms. Leave work 5 minutes earlier. Perfect your "sorry, im on the way out, can you email" response if someone tries to stop you when you leave work. Make a note of dates. It's easy when you get in the swing of things.