Tip of the Day: Beginner Tips #3
When placing your tongue on the face of the harmonica for the tongue block embouchure, use the tip-top of the tongue (the top of the tongue just past the tip). Since your tongue is commonly blocking the holes to the left (except for hole 1, where your tongue is at the right), you do use a a slight amount of the right side of the tongue, but not much... it's still mostly the tip-top (if you feel like you're using only the side of the tongue you'll need to adjust this).
Next... you guessed it... a light touch. It's imperative for tone, movement and pretty much every other technique we could speak about. If you find yourself needing to push the tongue on the face of the harmonica in order to cover enough holes, you need to use more of the top of the tongue, which is wider and will cover the holes well without using any force. Basically speaking, the more holes you need to cover, the more of the top of the tongue you'll use.