how do you find sponsors for your blog?
Why no one says Adsense?
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For eg...if you have a blog about laptop technology or something along those lines, you could probably try emailing the marketing division of hp (or a company with a similar niche- lenovo, dell etc) and ask them about opportunities that they are willing to offer- if you're running a competition, they may be willing to give you a couple of laptops to give away to the winner.
But first and foremost, you really need to have an extremely popular website!
You can earn more by selling links and blog posts of your blog.