Web accessibility can be hard to understand and time consuming to implement but a well trained accessibility expert with lots of experience would be able to work through the WCAG 2.0 success criterion quite quickly and easily providing great value to a website from a usability and accessibility viewpoint. For the rest of us that aren't as experienced, little hints and tips to help improve our designs and websites is what it will take to improve accessibility in our own sites one step and success criterion at a time.
Colour contrast and font sizes in our designs are one of the easiest things we can change and improve in our designs. It doesn't only help users with vision impairments but can also help improve the usability and readability of your site in general in many situations.
Take the scenario of a person reading an article on your website on their mobile device in the sun light. The glare on the screen will make it fairly hard to read but a site with a good text contrast ratio may still be fairly easy to read in such a condition.