Depends on how fit you are to start with. Will need to start very easy and build up if you aren't already running on a regular basis.
Do you have a target pace in mind?
In general you want to get in one "long" run a week that is much longer than your race distance and much slower than your target pace, and one "speed" workout, usually intervals at a pace much faster than your race pace. Fill in the rest of the week with runs of easy to moderate intensity to make up the mileage you want to get. Each week make the long run a little longer and the pace on the speed intervals a little faster.
Running is weird in that you can get fast by training slow, if that makes any sense. Google "VO2 max" and "lactate threshold" for better descriptions than I'll probably be able to give.
He gave good advice. I was a sprinter in high school and college. Your intervals should be something like 10 x 400 meters or 6 x 800 meters. In between 10 x 400 either walk fast for 200 meters or jog slowly for 200 meters. For the 800 meter repeats walk fast for a 400 meters or start walking and break into a jog slowly for 400 meters. I prefer a track. Some quality treadmills can be used for intervals.
Another successful approach to intervals are fartlek. It means speed play. You go out running slow for about a mile or two. Then just pick an arbitrary land mark like a telephone pole 400 or 800 meters away. Red line to that mark then relax and jog slowly till you find another arbitrary land mark. You really go by feel doing this. You judge when to red line it and how long to rest in a slow jog all by feel. It doesn't matter if the finish is actually 100 yards or a half mile. Mix it up and of course it's not exact. It's a great way to get your speed day in.
To run a long race like a 6 miler you really have to rack up the miles. One of the pit falls to watch out for is constantly running long and slow. I have seen it to many times. If you train slow you will run slow. The spring just goes completely out of your legs if you constantly condition yourself to run slowly. Your one day long a week could be something like a ten to 12 miler. Do not do more than one long and slow day week.
A recreational runner could do something like Monday 5 miles; Tuesday 3 miles; Wednesday 7 miles; Thursday 6 x 800; Friday 2 mile; Saturday 10 slow miles; Sunday rest. Don't stick to a rigid schedule like you have to stick to a script. I'm guilty of that with lifting. Just like lifting you will have bad days and you should be able to adjust on the fly. If you planned the day before to run 5 miles but you are not feeling it; then go for 2 mile run and call it a day.
