To put it very simply and without getting into any trouble it is this: simply don’t masturbate or have sex to climax. I mean, do either of these things as normal but just don’t climax.
This produces vivid, sexual dreams more often and as we all know, the more vivid a dream is in the first place the more likely you are to become lucid in it. Plus it gives you a very easy to recognise (sexual) dream signs: eg: would I really be with this person/these people right now?
It does seem very reliable in my experience. Maybe it has a connection with the Tantric theories about sexual energy leading to higher levels of consciousness also. I don’t know. But it honestly works surprisingly well.
Hopefully this topic won’t be closed as I’ve tried to ensure it’s as clean-cut as possible given the nature. Cheers!