Often, as travelsketchers, we just need a quick method to capture a moment. So lets look at simpifying a landscape. Consider this sketch that took less than 5 minutes.

It easily could have been done without the person, I added that on a whim at the end. Here is the basic technique:
- Paint sky, distant hills or mountains, and foreground with watercolor. Then let it dry.
- Draw in the trees with a pen.
- Add some detail.
Here is a video of the process, I recommend slowing down the playback speed.
Use a light gray-blue for this time of year on the sky, Then a darker, blue tone for the hills. Do both in broad strokes with a large brush, no detail needed, just shapes of color that approximate what you see. Do the same with the yellow ocher for the field in the foreground. Let the paint dry, it should not take too long since it is a thin coat.
Use a Micron of at least #3 or higher for the trees, or a fountain pen as I usually do. Notice I drew the trunks first, then the branches. The tree on the left is a bit closer to the bottom of the paper and thicker thus making it appear closer. Also notice that many of the tree branches come out directly opposite each other, that is because many of these fir trees will have one set of branch growth per year, all on the same level. Which, by the way, is a good way to estimate the age of a tree, just count the levels. Don’t be too precise, when you look at a tree you do not think about each branch, you see the basic shape – scribbles are perfect.
Then I used ink for some definition on the hills. A dark bit of squiggles on the horizon gives the appearance of some kind of growth but more importantly adds depth. A few horizontal random lines gives texture to the field.
That would have been enough if I was just capturing a scene while out walking, but I decided to add a person, and a couple of crows flying just for interest.
Since we are capturing the moment just general shapes and sizes are sufficient. I hope you will give it a try.