Navigate to a point from where you want to take the picture.
In the Advanced section of the Ensacpe settings you can enable the Architectural Two-Point Perspective, which will allign the vertical walls with the edges of the picture.
In order to get the part of the skybox in your picture that you want, sipmly use the slider in the Enscape settings.
Adding Depth of Field adds a great effect in blurring the foreground. This gives the impression of a good photo camera and lets you focus on the important part of the rendering.