I don't do long distances since I get bored, but I run three-four miles at a shot three times a week. I don't expressly do HIIT but I do sprint to exhaustion in the middle and end of my runs.
I also bike 45-50 miles a week, which is another great exercise for cardio that can serve a dual purpose of getting you to work or school or whatever. It has the added benefit of balancing leg strength since it targets different muscles than running and is a lot easier on your joints in terms of impact.
I have pretty awesome cardio with this regimen. For most people I've tried to help out with getting in shape, the problem isn't any secrets to technique, it's simply putting in the time and staying regular.
Everybody good, plenty of slaves for my robot colony?