Watching movies can be very helpful. Just get some ideas from the theme and make a song out of the topic.
Personal relationships. It might be romantic or chaotic, it is your chance to make songs from your experiences with that person.
Read History. Life of the national heroes, Presidents, cultures, colonization and many others.
Latest News. What is happening now is like for example the Covid19 pandemic is affecting the people’s lives all around the world.
Lastly, be open minded, be inspired, and inspire others. Life is give and take. The more you give the more receive.