You may want to try to sketch what you see as closely as possible, and light can make a big difference here. Hills and mountains in the distance may appear higher, simpler, smaller and, if you’re working in color, perhaps bluer or cooler as well.
You can utilize this aerial perspective to give your sketches a sense of depth. Choose your medium to go with the subject or with the amount of time you have. Play with color and texture to express what you feel about the landscape. Take a peek at how Canadian artist Marc Taro Holmes interpreted Sugar Loaf in Rio de Janiero, and then how Australian Liz Steel sketched the same subject. The styles are different, but both captured the feeling beautifully.
Marc Taro Holmes used very little pencil underdrawing (if any at all) in his quick interpretation of Sugar Loaf.
I chose to use a lot of linework to suggest the ruggedness and eroded peaks of the San Gabriels in California before I added watercolor washes. I took my time and paid attention to the planes and textures I saw across the valley.
Liz Steel used just a bit of brown ink as a guideline and then splashed in color freely. Notice how she suggested the skyscrapers and other buildings at the water’s edge.
And, of course, there are exceptions to any rule (they really are only guidelines when it comes to art). No one can tell you what you should sketch, or how. Let your eyes and your soul drink in the scene, and respond from your heart, not your head.
Explore ways to express texture. Your paper surface can help with this. Explore a rough paper if you want to depict a rugged surface. Use a dry brush in watercolor or skim the high points of the paper’s surface with colored pencil or graphite. Values create the illusion of volume and shadow.
I felt the need to zero-in on the mammoth Nevada rocks while the farther hill was in shadow. To capture some of the linear aspects of rocks in The Valley of Fire, I used my brush with the sharpened end, dipped it in a strong wash of color and drew with it. An old bristle brush, meant for oil paints, worked well to spatter some additional texture.