I usually find and negotiate for the public records we need to document a tip or an idea. Very few are already on the Internet. Instead, I have to figure out who in government has written something down, how it's recorded in computer systems, and then file Freedom of Information Act requests for the portions that are available to the public. Once I get them (or IF I get them), I usually go back and forth between what I think of as field work and lab work, refining the way I look at the data or finding new or better records to avoid pitfalls and take advantage of what the data can tell us. Then I'll go back to the experts, like the Agriculture Department's chief economist, and have them vet our findings.
The idea is to lead the reporting toward good examples, check their accuracy, and then use them to analyze the data to make broader statements. I'll write the sections of the stories or sidebars that I've reported as well. I work a lot with our graphics department to summarize the data, and, more recently, with our online colleagues to make the graphics interactive.