Do not write just for the sake of complaining. Blogging is your chance to get your voice heard and to speak your mind.
That does however, not mean that you should use your blog just to complain about everything and anything. The TV program, your breakfast, your salary. Blah blah blah…
Try instead to find a niche and to stay with that niche. Do not just whine about this and that. Find a niche that interest you and write everything about that subject that comes into your mind.
Music, movies, computers, sport, or perhaps marketing. Pick your own favorite and stick to that niche only, and you will be more certain that readers actually will follow you.