Classically, the forest base may be associated with green grass and bushes, but when you take a hike in a dense forest, you'll notice the greenery is much more sparse as the trees steal most water and sun. Coincidentally, the muted down oranges, reds and yellows will enhance the greens and brighter yellows on the mini.
After gluing the minis in place, sculpt some random shapes with Milliput, flatten small blobs, add texture with random strokes of silicone brush. Alternatively, you can cover the base with a paste or use other methods. Try not to cover feet, if you need, only
Stipple with Rhinox Hide , Medium Rust , Beasty Brown , Camouflage Green - use more darker colors towards the shadow areas and back of the base, and lighter towards the edges.
Mix in a bit of Pastel Yellow to Beasty Brown and stipple the edges of the shapes, add more of the Pastel Yellow as you stipple in the very edges going to around 1:1 mix (lightest values shouldn't be too bright to keep lightest values on focal points of the mini).
Using thinned down PVA glue, sprinkle some tea or seasoning like oregano or other earth tone bits.
Glue in whatever tufts or plants (I was using laser-cut paper plants).
Underpainting
It's important to spray from light to dark, otherwise - depending on paints you use - colors might come out a bit dull and dirty.
Prime black, then spray white zenithal in controlled way, ideally through airbrush with white ink. Work on localized values to accentuate focal points like heads/shoulders, weapons, not just flat top-down spray.
Spray from top with thinned 1:1 mix of [AK Blood Scarlet ink] and Bloody Red , spray a bit more than a half, because later it will blend a bit with purple
Spray shadows, recesses and from bottom with thinned 1:1 mix of [AK Night Purple ink] and [AK Dragon Blood], try not to cover too much of the red. Leave a bit of original grey from zenithal on the base
Spray the base and the very bottom of the mini with [AK Ocean Blue ink]
Leafs
Base leafs with Russian Green .
Add some Olive Green mainly to those facing upwards or in upper parts of the mini.
To the leafs that need more focus (on the capes, shoulder, etc), add Lime Green with "heavy" edge highlighting, to those lower, you can add delicate edge highlighting with this color
Edge highlight top leafs or most important ones (near focal points) with Pistachio .
Optionally, for sharper look, edge highlight with Pale Yellow , and then add Pistachio for more saturated and crisper edges.
Mini painter first, Age of Sigmar player second. My two main reasons to go bankrupt are Orcs and Nurgle, but Gitz and Skaven might join the list soon...