I can write a blog post about that because it is a really vast topic to cover in a few sentences. The basic idea is to just take your time to build your blog by using quality content in a niche with low competition. You will need to get backlinks, and it would be really hard to do so in the beginning. In the long run, you can get your blog noticed and start earning some serious cash.
I don't think that I should mention this golden advice here, but I am going to do it anyway. I recommend choosing a really small niche like a blog about taking care of your pet rats. You can promote products related to rats and earn commissions.The smaller niches will be much easier to rank for if you choose them wisely.