Whatever lawn or garden you have at home. Try to make it green. Because if you advise something & yourself not acting upon it. It will not be effective at all.
Then you can write articles for news paper & V SHINE to create awareness.
Talk to your teacher and get his/her help & every week write a few words to say in Assembly.
Make some chats to show importance of planting trees.
Take a tour with your friends to a nursery to buy plants.
All your friends collect some money every month from your pocket money & buy a prize to give to that person who makes his home more green.
With determination Inshallah you achieve your target.