Sound

Can you move without making footfalls?
Without rustling your clothing?
Without the content of your pockets jangling?
Can you avoid pushing the air in front if you?

Even if your footsteps are quiet, the vibration from your step can carry through the floor.
Be mindful of this.

Use every opportunity to practice being quiet.
Listen to your breathing and your movements, to your everyday habits. Do you clatter and bang, or are you silent?
Use external sounds to mask your own movements.
Practice constantly.

Try walking on different terrain.
See how different types of footwear serve to mask or advertise your presence.

Go to quiet places whilst the world is asleep and learn the meaning of quietude.