There's nothing like a forest shrouded deep in fog, It's something that I've always wanted to paint. And using this technique has given me my best results so far.

Supplies

A Canvas (The size that you want)
Acrylic Paint (I used Black, White, Sap Green)
Paint brush (I used a flat, a small fan, a small round, a medium round)
Water
Finish (I used Matte)

Step 1: Background

Paint the entire canvas with white, then add a tiny amount of black to the middle and blend it out, try to get it a smooth and even gradient.

Don't go too dark or the trees won't stand out.

If your having trouble blending with a brush, try using your fingers, its messy but it works.

Step 2: First Layer

Mix a bit of black into the sap green to get a dark green.

Then, using the fan brush paint in the ground, don't start to close to the bottom or you'll run out of room.

Then, using a small round, Paint in the trees, I used black for this. (if your having trouble getting a smooth stroke mix in a tiny amount of water to even the flow.)

Once you have the trees the way you want, I used the medium round to add the shape of leaves, but you can use the fan as well, I made the leaves the same colour as the trees.

Step 3: Adding the Fog

Make sure the Trees are dry before moving on with this step.

Take your white paint and mix in water. I used a 5:1 paint to water ratio but you'll have to see what works with the paint your using. (I made mine a bit to white)

Then use a large brush or sponge to wipe the wash across the canvas

I used a sponge for this layer, but as you'll see on the later layers the brush streaks look better, like the light is streaming down.

Step 4: Repeat Step 2 and 3

I went with 4 layers, but you can go as many as you like.

With every layer the ground shouldn't cover the ground behind it, and the trees should become bigger, adding fewer trees as well, you don't want to block out the ones that you added before.

When you have one more layer left move on to the next step

Step 5: Final Layer

Paint the ground like you did with the layers before, and add in the trees if you want you can use a very dark brown, these trees should be the biggest, so don't add many.

Add the leaves like you did for the rest but this time dab the dark green over the black, then add a few touches of sap green blending it in just slightly, lastly add a few touches of watery white.

I did the same for the ground, dark green, sap green, watery white...

Step 6: Finishing

I added a black border to my painting, then I used a matte finish, but you can use a gloss or whatever you think looks best, I just liked the way matte looks,