A blog can make you money if you choose a niche that is hot - and monetize it. Some niche research will help you know what is being looked for. Secondly, within that niche, look for problems that your target market is facing, and aim to solve it by providing solutions. That's it in short.
You still need some traffic, probably paid ads, to make sure your audience finds your blog. Once they're there, you could capture their email and have them in your list, that way you continue marketing to them in the future. Of course, you'll need to offer them some incentive to convince them to opt in, such as a free report which they could download after opting in. Make that free report a thing of value to your prospects, something that will make them keep opening your emails. Ultimately, you'll sell them some premium products.
Aim for a long term online business, through email marketing. The money is definitely in the list.