I run between 20-30 miles a week (you wouldn't know it to look at me, but I swear I do).
I have one long run between 10-12 miles a week. I then do a couple of shorter 3-6 mile runs during the week.
I just do it. Even if you are "too tired" after your shift or on your days off, you just have to lace up your shoes and start. I have a hard time doing that sometimes, so I have a deal with myself: I have to run a mile. If I still feel like crap after that first mile, I can be done. Of course, once you go that first mile, you next come easily.
I don't really have any set days that I run, since my schedule varies. Since my long runs can take 2+ hours, I don't do them during a 3 day stretch; typically I just run 3-5 miles before or after work. Except for my long run, when and how far I run mainly depends upon the weather. Now that it's getting warm, I'll switch to running after work, and once it gets hot and humid, my after work runs will be limited to 2-4 miles.
I also work out at a gym that requires you to sign up in advance for classes via the internet. Somehow, just reserving a spot in a class makes me more likely to go. At least once a week after work, I go to a yoga class. Right now I'm training for my first half, so I'm concentrating on running, but after that's finished, I'll go back to doing yoga 1-2 times a week, weight lifting 2x a week, and kick boxing once a week, in addition to my running. I amp up my classes (hello, airconditioning) and decrease my total milage during the warm weather, otherwise I'll die.
I guess my rambling recommendation is that you just DO it. I don't have a schedule, because that doesn't work for me. I don't plan to always run after work: if I'm super tired, it's raining, I wasn't able to eat before the end of my shift, well, a run is not going to happen. I have discovered that what works for me is simply having weekly goals, being flexible, and taking it day by day.