There's really only one key difference between typical portraiture and PJ-style portraiture: context.

Don't:

• Shoot close ups, where only the subject's face is in the frame
• Use narrow selective DoF to isolate the subject from their surroundings.

Do:

• Find natural subjects. If you want a picture of a doctor, find a doctor, don't find someone and dress them up as a doctor.
• Shoot wide. I don't mean wide angle (although W/As are much better for portraiture than most forum photographers think). You must give the viewer context for your subject. Is it someone who works in a steel mill? I need to see the steel mill behind them. If it's a street vendor, I need to see that they're selling goods on the street, it can't be a picture of them against a blank wall with the title, "street vendor".
• Make it sharp. Not only must the eyes be in focus, the entire face needs to be in focus as well as our supporting items/backgrounds.

Photojournalism, the awesome, documentary/humanist style of photography so many of us enjoy, is like most photography: much harder than it seems. You will often need to go back time and time again, make your subjects comfortable and happy to engage with you. I have a couple of PJ friends and they put in weeks, months or years shooting a series of pics. Some of the people they've had pose for them have literally spent months saying, "no" before finally saying, "I'd like you to take my picture".