Started out by adding a white to black gradient from left to right. Then began my rough line sketch to get some outlines and composition. Then some quick shading and adding in light. You can very quickly get something looking halfway right just from those steps.
Did some more sketching of the ribs and a few more "vertibrae" of the tail. They took the longest due to them being the foremost elements and the oportunity to do alot with light and shadow in each one. More work on the head "plate" which was also important to get the smooth shininess right. Also, attempting to make the skin look wet or slimy.
The final "push" was finishing the tail and the details everywhere. Refining the dark and light and getting the right balance everywhere. Fixed the teeth which were a bit off up to this point. Lastly did some work on blending the background so the alien is coming out of the darkness. The final step was simply add a blue hue to everything which gave it alot of realism instantly. Really made it pop!