I've used this trick for years, and it has come to help me in situations of stress and anxiety. Especially if all you have between classes is 5-15 minutes, doing this will help re-center you.
Everyone's body is different, so what might work for me might not do the same for you. Figuring out what works best for your body is a game of trial and error. Listen to your body and go with what is best.
Here are the steps that have worked best for me.
1. Posture
Stand completely still and adjust your body so you stand up straight with your back upright, shoulders down, and your chin up. As for your arms, I find that letting them drop naturally works for me. Some people like to clasp their hands in front of them, but try both and see which one works best for you.
2. Walking
Begin walking and become aware of all the subtle movements that your body is making. Feel your feet touch the ground from your heel to your toes and let your weight distribute evenly. Walk at a pace that your body needs - not too fast nor too slow.
3. Breath
Let your breath naturally fill your lungs. Loosen your body. Allow your eyes to focus softly ahead of you, taking in as much of the periphery as comfortable. Let your mind become clear, and become present. Maintain this center.
4. Senses
Once you feel your attention drifting away from the sensations of walking and breathing, take notice of your thoughts, moods, or emotions.
When you are ready, begin to notice the environment around you. Become aware of your experiences of the inner world and outer in equal balance. Let your mind rest at a point of stillness, calmness, and clarity.
5. Stopping
Come to a natural halt. Allowing yourself to come to a stop, and just experience yourself standing. Feeling once again, your feet touching the ground of the earth; experiencing yourself and, finally, bringing this mindfulness walk to a close.