One lucrative idea for making money online is to start a graphic design business. However, you clearly need to have some graphic design background to get this off the ground. Take a course to learn the basics and the ropes, then ensure that you get really good before trying your hand at a site like 99Designs or Fiverr where you can sell your services to others.
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.