Nothing can change the look of a model train layout or diorama faster than scenery. Even a basic coat of color can have a big effect. Adding this scenery is quite easy and requires only a few basic materials.
Ground Cover - You can use a variety of natural and artificial materials to make scenic ground cover. One of the most common is ground foam. This foam comes in a variety of colors and sizes to replicate grass, dirt, bushes, leaves, etc. It works well as a base. Additional materials can be added on top to better replicate plants, rocks, etc. You can also use real dirt and gravel.
Isopropyl Alcohol - Use 70% Isopropyl Alcohol to pre-soak the material. This is available in pharmacies - you probably have some in the medicine cabinet right now. You'll need a spray bottle capable of producing a fine mist to apply the alcohol.
Glue - There are two options for gluing the scenic material to your layout; common white glue and matte medium. White glue can be used straight, or thinned. Matte medium is available at craft stores and will work just like thinned white glue but leaves less of a glossy film when dry. Pipettes, eye droppers or squirt bottles all work for applicators depending on the size of the area you're covering.
You can apply these materials on any scenic base. It is best to apply scenery in small patches. Cover a few square feet at a time, and you can complete a larger area in no time.
Before beginning, it is best to have your materials in hand and make sure the area is clear of dust. Mask off buildings, backdrops, and anything else that you don't want to get sprayed with alcohol and glue.