Blog to get more sales?
If you make a Blog and add some photos of yours, people will read it and see some of your photos. Maybe they really like it, are interested and love to snoop around in your portfolio. This can already result in a sale. Withouth the Blog, those people maybe would never have found your photos/portfolio.
Though I think that the Blog needs some good content and (maybe) needs to be helpfull for others. This way it will be more populair and more people will read it.
Next to this, the Blog will also be indexed by search engines. Which can result in people finding your Blog on Google or other search engines. This also can also result in some sales of course.
Often there are photo request on the forum. Maybe there are people requesting something you have in your portfolio.
For example this one on the right.
Photo credits: Michel Mota Da Cruz.