Most instructional materials lack instruction on some of the basic expression markings in music. One example is dynamic indications. As with ending a piece, dynamics are easily incorporated into any piece.
Before any student can start following dynamic indications, they have to know what the markings mean. I suggest starting with two different dynamic levels: Mezzo-Forte (a normal, full sound) and Piano (quiet). This way the student can begin to learn the difference between normal playing and softer playing while avoiding the tension that naturally crops up with louder dynamic levels. Because what we do musically is so tied into our movement patterns in both hands, learning dynamics like this often improves the student’s technique (a bonus!).
After the markings are explained, I like to have students practice them by incorporating dynamics into easy arpeggio pieces. I do this for three reasons: (1) Arpeggio pieces tend to be easier for students, freeing up some mental power to focus on dynamics, (2) the use of a variety dynamics is a great way to practice arpeggios, and (3) arpeggio pieces sound like a piece vs. a single-line melody. My students (in both group and individual lessons) have responded better to arpeggio pieces than single-line melodies.
When the two dynamic levels are mastered, the student can start incorporating some graduated dynamics (crescendos and diminuendos). Again the markings have to be explained, then I like to use arpeggio pieces again to practice the concept. Then the student can move on to incorporating more and more dynamic levels into their playing. After some simple graduated dynamic stuff is nailed down, it’s very easy to get the student shaping melodies so the dynamics rise and fall with the line.
If you use repertoire books, methods, or other anthologies that lack dynamic indications, I strongly suggest you mark some in for your students. I tend to write my own little pieces for students, all of which end up with some dynamic indication, even if it’s only one at the beginning.