My advice to you:
#1 Don't start threads, search. You are unexceptional as a runner. That means that on lets run, there are masses of information on the droves of unexceptional runners that came before you. Additionally, you can gain really solid information by learning about the training techniques of coaches with a lot of success (Jack Daniels, Arthur Lydiard, etc). Letsrun is a source for that. Jack Daniels has done interviews and talks that are on youtube. Both of these coaches have books. Learn the principles of successful training, so that you can apply it to yourself. Don't take this to mean that you should try and do what Jim Ryun did in HS.
#2 Don't get injured. You could beat a 4:00 miler in a race if that miler had his leg cut off. This is an extreme example of what I'm trying to say which is that if you stay healthy, you will be faster than you would be if you got injured. Better undertrained than overtrained, especially for what you want to do. Avoiding injury is unique recipe for everyone, but it means: training within your limits, preventive strengthening, and learning to tell when you can ice it and keep running and when you should suck it up and take two days off.
#3 Run more miles. People say different things about this, but in my opinion there is no simpler or more effective way to improve distance running ability. Run more than 4 days a week. I think 5 is the minimum number of runs per week to see improvement in someone who has already trained at all. You don't need to run doubles for what you're trying to do. A step you could reach by the end of the summer is to run 35 mpw in 6 days of training. A subset of this is to run long. A solid long run is good for training efficient fuel use and recruiting the right muscle fibers for distance runners, in order to give you strength at the end of a race (this happens when you get that wooden legged feeling at the end of a long run). At least that's my understanding from what I know of Lydiard, who had everyone from 800m and beyond run up to 22mi.
#4 Run some of your miles fast. Remember when I told you to learn about Jack Daniels. This is where that comes in. It doesn't have to be complicated, but you need to be doing some quality all the time and a lot of quality in season, if you want to run the mile. Tempos, fartleks, hills,(all of these can be structured or unstructured) and 5k style intervals are good base builders. In my opinion quarter mile reps are the one workout that milers can't afford to lose (in season) if they want to prepare themselves mentally and physically for the mile.
#5 Prepare mentally. For me this is the most complicated part. This could be disciplining yourself to actually do your planned running, or holding yourself back from injury and overtraining. Learning not to stress about DNR days has always been my problem. I also try not to focus on empirical results and work to accept and enjoy the process of training (running the race is a tiny fraction of your training time). It's not that I don't set goals or care about the outcome. It's simply that I've always had better results when I can step to line and be calmer. The race seems less significant if you've already a few dozen enjoyable miles that week. This isn't to say every mile and interval is a breeze. I try to take stock of things and remember that when I'm old, I'll wish I could still feel the gut-churning part of a hard repeat.