Check out this cool video of some of the practice methods implemented by one of Japan's strongest schools - Kyushu Gakuin:
In this video, their teacher - Komeda Sensei - first talks about Suburi, and how care must be taken for both the upswing and the downswing. You must use your shoulders as you swing the Shinai. The video then cuts to a student demonstrating a bad example, with Komeda Sensei correcting him.
Komeda Sensei interrupts the student to say that we must make sure to properly use the wrists when striking, and also to lift the Shinai high enough so that you can completely see. Also, the tip and blade of the Shinai should stay straight, and not fall to the side. Finally, he says that the downswing should be fast, and sharp.
Next he shows us a practice method for improving the students' Shiai ability.
Here, the two students practice Shiai for 30 seconds, however, they do so under the scenario that the white player is already 1 point in the lead. This means that the red player must do his best to take a point back in the short time, whereas white must do their best to defend.
Video from: tandhnet