Repetitive tests (Regression), critical business paths, tests difficult to perform manually (e.g., precise data verification), and stable features.
Identify the cause (environment, race conditions, locators). Isolate the test. Use explicit waits. Check execution mode (headless vs headed).
A strategy where test scripts read data from external sources (CSV, Excel, Database) instead of using hard-coded values, allowing the same test to run with multiple data sets.