A 5 minute mile is actually quite tough (regardless of what the letsrun.com crowd might say). Here are some things I have observed when it comes to achieving this...
1. Your 400M time has no bearing what so ever on your ability to run sub 5. Exception - if you cannot currently break 75 you have no chance in the near future. I know people that can run sub 55 and cannot run a 5 minute mile. I cannot in my wildest dreams run faster than a 67 400M yet I can still run a 4:55 mile. The mile is an endurance event and the training should be reflective of this.
2. The best indicator I have seen is the ability to run ~2:28 800M as the LAST interval in an honestly paced track workout. I.e., don't go intentionally easy during the workout so that you can make the 2:28. If you cannot run a 2:28 when relatively fresh you are not ready to try sub 5. If you can run sub 2:28 as an added 800M at the end of a workout you should go for it EVEN IF after finishing the 800M you felt like you were going to die.
3. Bad pacing is your biggest enemy in the mile. Do not ever for one moment think you should go out in 73-74 for the first three laps so as to put time in the bank. I recommend 76, 75-76, 75, <74. Practive hitting your splits so you can do it in your sleep.
4. It is the most amazing thing to run a good mile. Typically you have been mixing in 800M intervals at mile pace during your workouts and feeling like there is nothing left each time you hit the finish line. Then, when racing a good mile you come through the first 800M somewhat distressed but get a high when you realize you can continue. The middle of the third lap is the entire race. At this point you begin to get very uncomfortable. The key is to stay with it and trust the advice the experienced runners have given you. This advice is to disregard the distress and keep on pace. Believe it or not the discomfort does not get any worse. Hang in there with the sole goal of hitting the 1200 mark within a second of pace.
5. The last lap in a mile is the easiest part of the race. If you get there on pace you will have realized that the discomfort has indeed not gotten worse. It is also time to tell yourself that there is only 400M to go. Update this in your mind after each curve and straightaway. Only 300M to go, only 200M to go, etc.
6. DO not look at your watch at any point in the last lap. The strategy is to run by feel. Concentrate on staying at what feels like the same pace for the next 250 of 400M. Then, halfway into the last curve start your best all out sprint. In your mind and body you will feel like you are picking it up. If you truely are running your best mile you will in actuality really just be shaving about 1 second off of 100M (or running 4 sec/mile under pace).
7. When you hit your mile goal time it is one of the best feelings of any race. When you miss it you will beat yourself up for weeks.
8. Be sure to have a friend time your mile. When you cross the line you may not have the motor skills to stop your watch and your vision may be too blurred to read it.