I don't have a sketch for today, so instead I have three easy exercises you can use to practice and pass the time.
1. Photography: Go out to a park and take a bunch of pictures of the nature around you, and when you get back home try to recreate those pictures in a sketch.
2. Take a random scene from a book and sketch, or paint, it using your imagination to visualize the paragraph.
3. Same as two, only take the scene from a movie instead.(Much easier)