You can get pretty far with data graphics with just limited statistical knowledge, but if you want to take your skills, resume, and portfolio to the next level, you should learn standard data practices. Of all places, UK Parliament has some short and free guides to help you with basic statistical concepts. They provide 13 notes, each only two or three pages long that can help you with stuff like how to adjust for inflation, confidence intervals and statistical significance, or basic graph suggestions [pdf]. I like.
Statistical literacy guides for the basics
Shifting Incomes for American Jobs
For various occupations, the difference between the person who makes the most and the one who makes the least can be significant.
Top Brewery Road Trip, Routed Algorithmically
There are a lot of great craft breweries in the United States, but there is only so much time. This is the computed best way to get to the top rated breweries and how to maximize the beer tasting experience. Every journey begins with a single sip.
Life expectancy changes
The data goes back to 1960 and up to the most current estimates for 2009. Each line represents a country.