I am not very good at animal figures, but I make all of my own landscape models such as trees and rocks, whatever I need to make the base of the diorama. The materials I use are wire, paper, silk, preserved natural foliage and polymer clay, there are several different brands and I found a couple that I like, Sculpy for larger pieces and Fimo for smaller pieces. The difference is the sculpy is soft and doesn't hold fine shapes like the Fimo does, but Fimo is very stiff to work with. First you make the skeleton and then put the clay over it in layers, first the bulky shapes like the "muscles" and then the skin.
the molds are usually made from silicone, I use MicroMarc, two part formula and I just follow the directions, the same for the resin that I cast as the final copy, I use the MicroMarc two part RTV resins. They can be purchased at most hobby stores or online.
For painting I use acrylic paints from several different brands, I don't know what others use but I am really happy with my trees and plants.
There is a great book that I just recently purchased called "Creating Life-like Animals in Polymer Clay" By Catherine Dewey. I highly recomend it to get started. My problem is I want the figures too small for me to really work with, the more I try the more I am impressed with Ana's and others work and it makes me appreciate the time and effort they put into each figure.