A good event schema is invisible. A bad one is the topic of half the meetings on the analytics calendar. Here are the things we keep coming back to.

1. Treat your tagging URL like product infrastructure. It is not a marketing toy. Put it on the same uptime monitoring as your checkout.
2. Use a custom domain from day one. Switching later is annoying and almost always loses some history.
3. Hash PII before it leaves your server. SHA-256 the email, normalise it first, and never log the plaintext.
4. Keep a written event taxonomy. It does not need to be elegant. It does need to exist somewhere people can find it.
5. Version your container changes. GTM gives you versions for free. Use them. Future-you will be grateful.
6. Test in preview mode for everything. Including the things you are sure work. Especially those.
7. Reconcile with backend data weekly. A small drift is normal. A growing drift is a fire.
8. Write the rules down once. Tribal knowledge ages badly and cannot be onboarded.

None of these are revolutionary. They are the boring habits that separate teams who trust their data from teams who argue about it. The single highest-leverage analytics document most teams could write is a one-page event taxonomy.