Any miniature garden can be transformed into a themed miniature garden with the right accessories. I had a couple little TARDIS's and decided they would look nice surrounded by succulents.
This Instructable was inspired by Doctor Who and the TARDIS is the main focal point of this miniature garden.
Step 1: BoM
Items relevant to your theme (preferably miniaturized)
Pebbles, gravel, or marbles
Tweezers and/or other tools to help plant and move things around
Additional decorations (such as colored preserved moss)
Step 2: Succulents
With miniature gardening you are gardening "to scale," so you want the plants you use to be able to take on the role of a tree etc. A succulent that is twice the size of your main focal point will give the illusion of being a tree.
Additionally, contrast is extremely important. You want to use a variety of succulents because a bunch of succulents that are the same size, color, shape, etc won't give your mini garden any definition---it'll all look the same and possibly like a big mess of green.
Step 3: Theme Accessories
I had a couple TARDIS pendants that were supposed to be for jewelry making but are WAY too heavy and a dead cellphone light buzzer TARDIS that my husband gave me a few years ago. I ended up using the smaller TARDIS as the main focal point.
Whatever theme you go with, you don't have to have a TON of accessories. One or two items that can hold the theme up on its own is sufficient. The TARDIS is such an accessory. It's a character all on it's own and can anchor pretty much anything.
Step 4: Layers
The first layer of your garden will be the gravel/stones/marbles/pebbles etc. This is for drainage and to help the roots avoid soaking in water. The second layer is the activated carbon/charcoal. Third is the coconut fibers and last is a couple inches of soil.
How thick your layers are will depend on the depth of the container you're using, but the soil layer will always be the bulk.
Step 5: Arrange
I started arranging my planter by adding the TARDIS first and then positioning different plants inside the soil. I added a couple "mounds" of soil to emulate a hilly landscape and positioned various sided succulents around the TARDIS. I wanted the larger succulents to give the effect of trees and large bushes surrounding the TARDIS. I only added 7 different succulents to give them room to grow.
After positioning the succulents and planting them, I spritzed the surrounding soil with water and then added a couple pieces of dyed moss.