This is a simple but dramatic, one point perspective sketch done as a demo for my pastel students.
Whenever I have a piece that has one point perspective, I typically start out at the vanishing point and work my way outwards. Your lines in a one point perspective drawing can only go in 3 directions: vertical, horizontal or back to the vanishing point. If you are above the horizon line, your lines leading back to it will angle downward, if you are below it, they will angle upward. Forget memorizing this, just put it into practice a few times and it will become second nature. By putting it into practice, I mean sketching from life as often as you can and learning to see the perspective naturally. I can’t emphasize the importance of this enough. Once you understand and automatically see it, you can work from any source: photos, your on site sketches or as I typically do, a combination of the two. Remember, photos often distort perspective, you can include, eliminate or exaggerate as much of that distortion as you choose, as long as you understand the basic principles outlined above.