Evolve your manga drawings with objects and decorations
Whether your story takes place in an urban or natural setting, you must learn some techniques to represent buildings, trees, the sea, etc. Your manga can not only be made up of characters that develop in an empty world: you have to make them evolve in a suitable environment.
The natural environment is formed mainly by grasses that can represent thick, more or less leafy trees and rocks that go from stone to mountain.
The most important point to give details to your environment is the level of shadow: playing with light is essential to detail your elements such as trunks or rocks.
The sea is formed by a more or less flat extension composed in shades of gray to give an impression of depth. The waves are easier to draw in profile so that they stand out well from the rest, while those that crash against the rocks look like small explosions.
For urban environments, the main technique to use is multi-vanishing point perspective: start from a horizon line, then place your vanishing points on it and a third of the height, to place the tops of the buildings. Then you can detail them with doors, windows, etc.
To give your decoration perspective, you can also use the multiplane technique to facilitate depth of field. Draw on several pages the different elements of the decoration (from the furthest to the closest), then assemble your sheets to create a unified landscape. Use a palette of dark gray for the front and white for the background.
Finally, take examples to draw everyday or transportation objects that may be difficult to master at first. Start with the raw shapes, without details, before improving as you go, in the same way as the faces of the characters. Take your time and by dint of patience you will reach new heights.