"You are loved. Always remember that." Everyone has their own battles we know nothing about. These simple words can make a huge difference so don't forget to remind them that they are loved.
It won't also hurt to be kind and nice to people you don't really know but get to interact on a daily basis. Whether you are conversing personally, through phone or email, when you're out for groceries or you order food, when you're in line and you get your turn for any service etc. Be kind. Be nice. Make compassion and positivity a plague and you'll see how healthy and beautiful it is to be surrounded by happy people.