I don’t know how to write that word to really bring out the expanse of its meaning.
1. Anything related to the work you do – problems, solutions, facts, myths, people.
2. Anthing related to the work you “Love to do”.
3. Anything related to your hobbies/ liesure/ pastime/ travels/ activities/ memories.
4. Anything related to your friends, locality, city, country, region, religion, politics, laws, films, tv, schools.
5. Anything that is not related to any of the things I listed above. Abstract, Aliens, poems, sketches, photos, fantasies, dreams. You can even blog about blogging, or blog about not-blogging.