I don't have a consistent DD workflow. It really depends on the business and how well I understand it. Usually, once I have an idea, I try to figure out what the heck they do. Could be "business of the company" in a 10K or a website, or a call to customer service or sales or whatever.
IF (and only if) I can get a feel for the sort of business they're in, I try to get a feel for how they do it, how they measure themselves, and how they reward management. Usually start with ARs/10Ks going back a few years to get a feel for a business in transition (which is my primary interest), then presentations, check VIC/Distressed Debt/CoBaF/etc. for writeups, then conference calls of the past year or so.
IF (and only if) after finishing the above I have an idea what the two or three most important factors are going to be for valuing the company 2-3 years out, I'll try to value it and test my assumptions under very punitive scanarios.
I probably get a bit deeper in than most, but I really like trying to figure out what makes businesses tick. I take the 5-8 positions theme seriously, so my historical max position was ~40%, and a minimum investment is around 10%. Hey, after doing all this work, I want to get paid for it!
Luckily, it's my full-time job. Last year made a total of two (almost- one was just a shift in investing in the same co's capital structure) major new investments.
Probably the most important part of my DD is a two-week-or-so hemming-and-hawing period in which I pace back and forth in my office and try to talk myself out of investing. Usually it works. Has saved me a lot of pain. Also, helps me sleep better after having taken a position knowing I exhausted my arguments against it and have committed to playing the odds (whatever they may be).