Basic Trekking Etiquette which needs to be followed :

Respect the Environment and the Flora & Fauna. Do not litter or throw garbage on the Trail as we need to bring it back for proper disposal. Keep the Mountains clean and pristine.
Do not damage or uproot Plants on the way. Also stick to the Trails instead of shortcuts as it damages Vegetation.
Do not step into Rivers / Streams / Lakes until absolutely necessary.
Avoid all interaction with any Wildlife that you encounter on the way.
Kindly carry Sunglasses with UV Protection, Sunscreen Lotion and Lip Balm.
Kindly avoid Smoking , Alcohol or any other Narcotic Substance during the Trek.
Always ask for permission before taking any pics of the locals especially Kids and Ladies.
Do not make loud noises or play Music at the Camp sites or while on the Trek.
Avoid getting into debates which involve sensitive issues like Politics or Religion. Discuss the Mountains, the Rivers and the Valleys as much as you can.
Last but not the least Respect the Local Culture and avoid doing stuff which might embarrass the locals like PDA or wearing revealing clothes (This is for both Men and Women).