Question from my fiancé

So my fiancé has only made me cum from oral once in 2.5 years. Every time she gives oral she sucks me for a good ten to 15 minutes with no reward for her troubles. Last night she asked me for advice on how to make me cum from oral. I have only been with one woman who could consistently make me cum from sucking me, a Latina that I was with before her.

The only advice I could come up with was to stroke the shaft with her mouth and to stimulate the underside with her tongue instead of just sucking the head.

I know there are others that have this problem as I have seen your posts. If your SO asked you, what advice would you give them?