Make sure to only request the subscription after providing visitors with fresh and helpful information or after making them laugh. If you've done your job well, viewers who have just seen what your brand is about are eager to want more.
This is something anyone who owns a YouTube channel always include in the beginning and the end of their video content. It is more like a reminder for those who have enjoyed their content to try and support their project by subscribing to their channel and it works most of the time.