Increase in income is directly proportional to increase in traffic. How to increase traffic? A difficult question to answer indeed. A lot depends on what is that you are writing there and how many people across the world will be really interested in reading them.
One easy way to promote is through facebook. At least your friends and relatives might visit your blog through facebook link.
Twitter promotion is useless as per my personal opinion.
Alexa ranking is based on your page views. If page views increase, Alexa ranking will improve.