First of all you need to decide a scale for your diorama. This is important because you need to scale things up accordingly. For instance, a tree and a bull cannot be of the same size because it is not possible. Either set a scale according to your own perception or you can use a ruler to select the perfect height for different things which you will add to your model.
Secondly, collect all the material which is necessary to make your diorama. It could be palm trees, human figures, models, animal figures, doll house, furniture and other things which you think should be a part of your diorama. Make sure everything is as detailed as possible.
Make a background. It gets quite difficult to manually create a background scene so it is advised that you either paint a background for your model or print a picture. For instance, if you are selecting a desert scene, you can print a picture of sand dunes which you can paste at the back of your three-dimensional model. Make sure that the background images are aligned with the scale which you chose in the first step.
Select a container of your choice. Children mostly use cardboard boxes or shoe boxes to create a diorama at their home. However, you can select any box of your liking. A light weighted, yet sturdy box, is considered ideal for such a model. Light weight is a priority because there is possibility that you will have to move the model around.
Build your diorama by working from back to front. Start with the details at the back. Add the background picture and other things which should be at the back of the model. You can even use shorter models for things which are far behind. This will add a more realistic picture to your figure. Either use glue or a double-sided tape to stick the figures on your model.