pushing sketching boundaries

Lately, I seem to be on a quest to improve my sketching abilities. I have been challenging myself to push myself to become more detailed in my sketches. I have never done landscapes or nature drawings because I thought that I wasn't good enough to draw in that way. After thinking that I remembered what my art teacher told me, "If you can see it you can draw it." Now, when I start sketching something that I am looking at and I get stuck or lose my focus, I tell myself, "If I can see it I can draw it."