Your scenery has to work with trackwork to make the best visual effect. Your cars have to be the size and type that work best with your layout and scenery. More precisely, it is the amount of space and its shape. Indoor layouts usually have obstacles such as walls, water heaters, and other impedimenta. Outdoor layouts will have terrain obstacles, both natural and man-made, plus trees, shrubs, etc.
Obstacles change the shape of available space.
Space determines the length of straightaways, the best diameter curves and the general shape a layout might take. Good trackwork is a matter of implementing available space to allow the most varied movements, without being totally chaotic. Scenery for G comes two ways. Some is already there, such as plants, trees, rocks, garden structures, etc. The rest will be added later.