Indian etiquette considers it important to use a person’s title wherever it is possible, titles such as doctor or professor etc. Use courtesy titles such as "Mr", "Mrs", or "Miss" for those without professional titles and wait to be invited to use first names. Try ‘Sir/ Ma’am’ for strangers and ‘Uncle/ Aunty’ (or Chachaji, Mausiji etc) for familiar people. For a stranger who is not so old, it is better to suffix the name with ‘ji’, as a mark of respect.