Crackie has some spectacular art!
NSFW is fun (and popular)! The best advice I have is to figure out what you are most interested in drawing and look to artists that do it well for inspiration.
Maybe study their art a bit, do some breakdowns of what makes their art work. I looked at artists that I thought had elements of what I wanted in my art and I studied them while sketching.
Proportions are very important for making a character look more NSFW. I struggled with this forever, ha ha~
It's good to start with realistic anatomy. Learn how the body works so you can draw breasts and penises that have a realistic weight to them. Study porn if you want!
Once you have some studies down you can try exaggerating features to make them stand out or look more appealing. Don't worry about any backlash you might get for sexualizing your art. Exaggerating features, including erotic parts, is a key part of what makes art valuable. Crackie's art is so appealing due to the strong grasp of weight and exaggerated features for breasts.