I hope I don't offend you but you need to write content that is going to pull in people and ads that people will click. The most popular niches are.
1. Recipes, Cooking, and Food
2. Nutrition and Sports
3. Health and related issues , home remedies for health is popular
4. Weight Loss
6. Cars and Related Motoring Issues
8. Pets and related issues
9. How to Make Money Online
10. Movies and Games
If you can drill these niches down and find the sub niches you can do well. Its kind of like if you lived out on a busy road and set up a sea shell shop you might well have a few customers stop by and buy a few sea shells but if you put up a cheese burger shop you would have a lot more customers.