Final answer:
The first step in troubleshooting a misbehaving app on iOS and Android should be to restart the device, followed by other measures like clearing the app cache, updating, or reinstalling the app if needed.
Step-by-step explanation:
When troubleshooting a misbehaving app on iOS and Android, the first thing you should try is to restart the device. This can often resolve temporary glitches by refreshing the system resources. If the problem persists, you might consider other steps, such as clearing the app cache (for Android), updating the app to the latest version or, as a last resort, reinstalling the app. Remember, the sequence of these troubleshooting steps can vary based on the specific issue you're encountering.