Google offers many advertising products and many types of ad tags. But whichever type of tag you use, there are a few things to keep in mind.
Ad requests typically send a page URL to Google. So make sure there is nothing featured in your page URLs that shouldn't be sent in ad requests to Google.
In particular, please make sure that pages that show ads by Google do not contain your visitors' usernames, passwords, email addresses, or other Personally Identifiable Information (PII) in their URLs.
Some Google products allow you to add macros, such as the key-values feature of Campaign Manager, Google Ad Manager, and Google Ad Manager 360. Again, you must avoid putting anything into these macros that Google could use or recognize as PII. Failure to comply with this requirement will be treated as a material breach of contract.