Going down...

My fiancé is so bad at going down on me. We were both virgins when we met. He literally has no idea what to do down there. He's great at the whole sex part, but orally, this poor man doesn't have a clue. 
What can I tell him?! 
I've already asked him to try to do better or to try different things but it's just not working. And I don't know how to do it so it's hard to tell him lol
Help a girl out!!!