You can encourage them by telling the benefits of cleanliness and the disadvantages of dirtiness. You can organise a rally in your locality. You should encourage them to clean the locality. For example - In a small city Khandwa, a newspaper started a campaign. In this the people of the city were invited to clean their city for at least 15 minutes. And the people who registered to clean the city were called 'Safai Dut' of "City cleaning angles". And today the people of the city do not wait for the government workers to come and clean the locality but they clean it themselves.
HOPE IT HELPS !