1. In order to limit the number of issues appearing in production environments, user acceptance testing or pre-production testing must be carried out in an environment that matches production environments as much as possible.
2. Data volume, Salesforce Processes (Triggers, ProcessBuilder, etc.) and Salesforce security settings should match what will be seen in production environments.
3. UAT should be carried out in a "non-preview" Sandbox Org as Salesforce updates included in a preview Org may not be compatible with a previous release.