Experience. Whatever area you want to work in as a consultant, you must be able to show clients that you’re qualified to advise them. If there are organizations related to your field, make sure that you’re a member of them. Similarly, if you can take a course and become certified or registered in your field, do it and then add that to your credentials.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.