A lot of times I will get asked on how exactly you're supposed to sponge and I don't know if there's any true technique however the one that's always worked for me is to dab across your area and then when you go to add color in dab your sponge in the ink, then sponge onto scrap paper, and then for your second layer come back onto your paper with circular motions.
To achieve the look of snow hills I simply cut out a scrap piece of paper with a wavy border and used that to block my Ink and create the White hills. Start with the top hill and then add the second hill below it making sure to only Ink the top of your stencil not the entire area. Notice how the middle of my hill is still white.
Those trees are from Just For Fun and are called Evergreen. JFF has a number of wonderful stamps that would work well with this technique and I cannot wait to try it with some other ones.