Challenge each person to make two or three changes in the way they use energy for one month. Have them keep track every day of their efforts. For example, post a sheet of paper beside the shower and have each person record the length of their shower. When the utility bill arrives, enjoy the results. You've probably put money in your pocket.
Every recommendation here applies to renters as well as homeowners.
If rent includes utilities, you ultimately pay for higher energy bills in rent increases. Get permission from your landlord before installing any energy-saving devices. You can take these items with you when you move. When you look for a new place to rent, consider energy costs. Ask the utility company for monthly energy costs for that address.