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
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When Straight Americans Lost Their Virginity
Everyone has his or her own timeline, but here it is in general for Americans.
Salary and Occupation
Salaries vary across occupations. Here are some charts that show by how much for 800 of them.
Years You Have Left to Live, Probably
The individual data points of life are much less predictable than the average. Here’s a simulation that shows you how much time is left on the clock.