itch.io

For that job, they need to have over 45 lewdness or their gold will be halved, that's specifically what will cause it to say they had insufficient skill. So advanced sexual actions is mainly just being super lewd. However, doing kinkier stuff with them causes their lewdness to go up faster.

Then there are bonuses from Sex-crazed, hollow nipples, augmented tongue, and nympho.  Nympho also lowers the stress gained (or if they're a bunny).