At first I would like to point out that the technique I used for making this concept contains some components and aids made in 3d software. To follow my way of working, it's necessary to be able to work with any of the 3d software and have advanced skills in Adobe Photoshop. This tutorial explains effective principles on how easy and fast it is to reach the high quality concept paintings. I hope this will inspire your own work.
Adjustment of Composition and References
Personally I like to combine available digital means - painting with a digital tablet in Photoshop, matte painting and using 3d objects as reference. It is the best way how to hit the ceiling during short time. It is applicable for concepts, final pictures even for illustrations.
At first I generated a really simple low-poly 3d model. During rendering I am trying to find the best position agreeing with my vision of final composition. Where necessary, it's possible to add some guidlines and perspective lines in Photoshop to a rendered scene. the use of this aid covers many advantages : it performs a function of first sketch, where I draft a composition, perspective and lighting. For a person who has just a little control over 3d software this way means a big help. And of course it improves the final face of a picture. If you can not or don't want to use 3d software, you can natuarally use your own way.
Note: Don't Forget to render the image with alpha channel. You'll avoid a complication with masking the scene manually.
This is a rough 3d model, I used as a sharp reference. (I'm not going to do tutorial how to model in 3d. I'll only remark - person, who can use 3d, he is able to make this within 30 to 45 minutes.
Painting and Adding Details
Now I am focusing on some picture examples with descriptions of the most necessary operations in this stage of work