I find that by putting together your own knowledge of a topic, the knowledge others such as family and friends can give you on it, overheard conversations about the topic, and research on the topic, you can write about a certain subject fairly easily.
I do have to do some research before writing about some of my subjects, and it’s always good to do that anyway just to make sure you have a pretty solid grasp on what you’re writing about.
Also, you mentioned writing about just your own experiences. Well, there’s a great quote that disputes the idea that writers should only write about their own personal experiences.
"Writers don’t write from experience. Writers write from empathy."
-Nikki Giovanni
:)