I started running a couple months ago, and the best thing I found was to push yourself with speed and distance, but you have to realize when you're pushing too much.

When I started running I would run 4KM two times a week. (Keep in mind I'm in the gym 5-6 days a week, plus I play hockey once a week, and ball hockey once a week (essentially all running))

Once I felt comfortable running 4 I tried 5, then 6, then 7, 7.5, etc...

Once I hit a plateau (around 10k) where I couldn't keep my running consistent, I ran at 9-10k for about a month to try and improve my speeds.

I'm not sure if you'll find this relevant, but this is what helped me.

I don't run anymore because I landscape heh.

http://www.coolrunning.com/engine/2/2_3/

Couch to 5k is one of the best resources out there for beginning. You're already at the 4.5 - 5 mile mark, so it might not necessarily apply.

If you're doing purely running (unlike Lights), work on increasing the days per week, then work increasing milage. At least 5 days a week is generally recommended, though don't rush it if your body isn't ready. If those extra days are tough, do them at a slower pace and/or less milage. Beyond that, I don't have good advice since I've never trained for beyond an 8k (and never probably will). You can probably google a good guide for advice on what to run each day.

EDIT: Words

If you don't have a time goal in mind then just work the distance up in increments of your choosing. If you want some specific workouts you can do something like mile repeats, take a time that you can pretty comfortably run a mile in (ex: if you run a 6 minute mile go for 6:45) and run that 4 or 5 times in a row with ~2 minute breaks in between. It should build your endurance pretty well.
Here's a link too: http://www.halhigdon.com/training/51130/Half-Marathon-Training-Guide

I will echo what #3 has said, running everyday is far more important than increasing your mileage. I also recommend running for time NOT distance, distance teaches bad habits, IMO.

As for an actual training plan, I can give you a very bare bones outline. With where you are now, try running for 20 minutes each day (stay a minute/mi above your expected race pace, it should be a slightly uncomfortable run where you are just able to maintain a conversation with your (non-existent) running buddy. Once, the runs for a week become simple, i.e. you feel like you could go for much longer, bump up the time by 10 minutes. However, do not increase your run loads each week, wait at least two weeks before increasing your time.

Continue this up to 50 minutes. Once you can reasonably run for 50 minutes then you can have some fun. Set aside two days each week (hopefully decently separated from each other) one for a "workout" and another for a long run.

The workout should be repeated running at race pace (or faster, just make sure the pace is consistent). My favorites are running multiple 800m's on a track with a rest break of how long it takes you to do one (run one in 1:30, rest for 1:30) and laddered fartleks, where you jog for x sec, then run for x sec(at race pace or faster), then jog for 2x, then run for 2x, etc., up until you reach the point where you wished you had never decided to run a marathon. Then work your way down the ladder until you finish running at x sec again (e.g. x, 2x, 3x, 2x, x).

The long day should be a run that is at least 1.5x more than your normal days, if you run 50 normally, on your long day try going for at least 70.

I also highly recommend that you keep a running log of your time that you ran, your distance, and your pace. Also, try finding somebody to run with, while having a running plan is great, nothing gets you out the door more than a friend who is waiting for you. Mix up your running trails as well, nothing gets more boring than running the same path every day.

Source: I ran in highschool competitively and college (with a club) and have sub 3hr times in marathons.

I go to the gym about 3-4 times a week and I'm on the ice for hockey about 3-5 times a week, I hate running but unfortunately it's something you kinda have to do. I'd say in order to run for a marathon, run for long amounts of time or as much as possible. Don't worry so much about distance. If you are conditioned well enough, the distance wont matter so much. You have to make sure you stay running as much as possible. Don't let a few days go by without running because you simply did not feel like running.

#1, I ran a half marathon last Saturday the 15th and I finished in 1:22. I run for my high school, so I am regularly going through semi rigorous training. If I were you, I would start to increase my mileage weekly (or even bi-weekly) by about 10%. I will also go off of what #5 said and also try to run for a certain amount of time. I would plan on running for the amount of time, not the amount of distance you plan to run for once or twice a week and keep track of how long you are running. For proper training, I would also try to run a half marathon distance at least once before your race. Not at race pace, but just a little slower than your training pace. Lastly, you should try to add one day of running to your normal running schedule. So if you are running 4 days a week now, run 5 days a week for the next two weeks, and then run 6 days a week. Don't run all 7 days of the week, because then your body won't have time to recover. I hope this helps. Good luck!

Hal Higdon is good, I suggest you use it. If you can already run 5 miles you should be in great shape by the end.

#7 covered it really well, intervals are good if you wanna hit a specific time but if you're new just running distances of maybe 5-22 kilometres a few times a week should do it.