It's really great for a first time. Here are a few things you should try to improve first:
General: -The anti-aliasing isn't strong enough. It looks okay on pic 8 because there's a background, but it's really a problem for pictures with transparency. Rendering to an higher definition would also be an easy way to improve quality. It will increase render time, but it will take almost no effort from you. -Your textures sometimes don't look really good. The walls (especially the brick one) would look better with random shades thrown on it. Adding some relief (like, cracks and irregularities in the stone) would also be great. Also, clothes and the dragon's skin look a bit stretched. Using higher definition textures would help. If you can't, making boobs smaller, like in pic 14, would probably fix it. -Your smiles are creepy.
Pic 1 to 5: -Her position looks awkward. Her legs are too straight, and her hand placement is weird. Either make him hold both of her forearms at head height, or put her hands on his penis. -Her hair is clipping. -Her mouth looks weird. Look at Vaesarks galleries (/g/612479/01acfd1f2f/ for instance) and try to improve this. -Adding a few pictures with the camera closer to the main action would have been great.
Pic 6 and 7: -There's grass clipping through the stone.
Pic 8: -There's an ugly angle on the rock, it looks like it's made of two pieces soldered together like in cheap plastic toys. Try to make it look smoother. -A slightly warmer light source would make the scene look more natural. It looks like the place is lit by neon rather than torches.