It depends on the age. It doesn't do much good to show a 5-year-old statistics showing that a person's earning potential increases in proportion to their education, but that might help with a teen deciding whether or not to go to college.
I think the best way is by example. For some parents, it might be too late to get an education (you might have dropped out, not finished college, etc.) so in that case, you could say something like "I dropped out of high school and the best job I could manage is cleaning highway rest stops." Also, just because you might not have gotten much education doesn't mean you don't value it. If your children see you reading, watching educational TV or bettering yourself in other ways, they pick up on that and follow your example.
Another tactic, especially with kids glued to the computer or video games, is to remind them that the people who made those things possible were had good educations.
Short answer: show them the evidence; lead by example.