Testing the audio is important—they should listen on different speakers or headphones to see how it sounds. Sometimes a certain phone might muffle some effects, so testing across different devices ensures the prank works as intended.
But I should also mention the responsibility part. Making sure they know not to use this for harassment or in a way that could hurt feelings. Trolling should be consensual and light-hearted. Also, some technical troubleshooting—like making sure the audio isn't too clipped, managing headroom to prevent distortion from being too harsh.
They might also want to know how to combine effects. For example, applying a low-pass filter to muffle high frequencies or using flanger to create movement. Also, maybe using a vocoder if they have two tracks—one for the carrier and one for the modulator—to create robotic sounds.
Wait, the user mentioned "best friend," so maybe they want to keep it within a good-natured prank. Maybe suggest setting up a loop of the distorted audio to play on a friend's device or sending it as a voice note. But again, emphasizing the consent aspect.