It helped us a lot to work on communication between alters, just having that line of communication made it much much easier to share memories of events, most times passively. It’s taken us a long time to get really good at it, so it’s a bit of work, but it’s worth it to get to know the rest of your system and really talk to them so you can chip down those barriers

We've made a habit of writing down anything of significance. Also the app Simply Plural might help

We've taken to writing a lot down in notes apps or sticky notes, although in some cases around certain people we've taken to avoiding as many incrementing comments as possible (attempting to not ask questions like 'didnt we already do this/been here? Etc') anything you think might be important, definitely take the time to write it out. Journals are also great for that.

We have a private discord server where we each journal every time we switch. Sometimes though things fall through the cracks. Like someone scheduled us a doctor appointment and didn't leave a note about it so we called to schedule and they informed us we already had one set.