Here is a step-by-step tutorial on how to sing "How Not To" by Dan and Shay:

1. Start by listening to the song and getting familiar with the melody and lyrics.
2. Practice singing along with the song until you feel comfortable with the melody.
3. Try singing the song without the music to see if you can remember the lyrics and melody.
4. Record yourself singing the song and listen back to it to see where you can improve.
5. Practice singing the song in front of others to get feedback on your performance.
6. Keep practicing until you feel confident in your ability to sing the song.