3D scenes

Here in this forum , i see a lot of great 3D scenes made in blender (cycles) and i want to ask those you have knowledge about creating composed scenes. When you start creating scene (for example ->house the forest) where do u start from? Do you first place everything and then render each objects or you go one by one rendering or do you render each object desperately and use Ps,Gimp to do kind of like matte panting/composing?

No, never use GIMP or “fixup” techniques.

I start with the subject of the scene which is typically the foreground element. Then add in background or midground elements as needed. If you are not aware of the rule of thirds, look it up. Camera placement or camera move comes early in my scene development. Material and light tweaking comes last.

Any means are good to get to the finish.
Say, i had a scene and decided on night skies background… Quick star field is taken out from the blender and all i needed was just a notion of stars in fact. I could create another Blender scene and render some particles, texture gradients and what not, then take that and composit two scenes… Why? It was much easier and faster to bring render and mask into Gimp and finish image there.
Be efficient. Use all available tools.