Make a pic of you licking your girlfriend's ass

Check out any magazine or book with pictures of the type of photo you want to take and use the pictures as your guide. If you're speaking of hard core porn, just shoot what you have and don't worry about format; content is king in that case.

Otherwise, simply pay attention to the rule of thirds. Divide your rangefinder (ultimately the picture) into thirds up/down and across. Think of how the picture will be viewed and consider that most folks read top-to-bottom and left-to-right forming a "Z" or "Zed" pattern which is the same way they interpret photographic information.

One aspect of visual data ingestion is motion. Gaze motion follows the Z pattern and is the motion that the eye needs to follow across and down the photograph. Images that draw your attention (Gaze) to the subject (say your penis or cunt) have gaze motion working in their favor. If your subject is your penis and it is not in the normal Z-pattern flow, will have the viewer disliking the experience, even if the photo has a great subject.

Remember that a colorless (gray scale without variation) photo is uninteresting and has little interest to most people. Too much skin, all the same color, is uninteresting. Use some color to highlight the subject but don't put too much clutter in the background or your viewer will not be able to focus on the subject of the picture.

As for settings, find a pleasant location that you like and shoot against it. Again, keep the background simple and contrasting to the subject of the photos.

There are many books-worth of photo tips but if you find a picture you like and give it your best effort to simulate the subject and background while following the rule of thirds, you should turn out interesting photos. Photography 101 stuff. Good luck.