Yeah, you need to focus on something you enjoy doing and you will enjoy talking and writing about as its proven if you don't enjoy doing it. It wont last.
Narrow down your niche as far as you think it should go and start reading up on it, research, brainstorming and gathering ideas. This is the most important step when creating your site so don;'t rush it to much.
Get back to us when you've thought of an idea