If they can get you asking the wrong questions, they don't have to worry about the answers. "Gravity's Rainbow," Thomas Pynchon (1973)
Sometimes when an athlete comes asking a question, or makes a comment about something lacking in their training, they tend to present the question in the form of their own desired solution. People who love long runs will frame their question so the answer is more likely to be "long runs." People who like intemediate-to-long distance repeats will frame the question, hoping I will answer with their preference. However, there are more important questions which need to be asked when it comes to training.
I like to start by asking the person about the amount of time they can comfortably set aside for run training without drastically affecting their work, their personal life, the interests of their fellow family members. Available time also affects the body's ability to recover from training stress.
Work is the most obvious limitation when we talk about time constraints. Since our town has several military training bases I occasionally work with semi-accomplished post-college runners. Most of these young men & women don't need me to deal with the small details; just provide a few good workouts while they're in student status. Some are good recreational runners who want to stay fit and train for a few races. I usually remind them the life of a military student is well-filled once they start their course of instruction, but I've always made myself available to their needs. As for civilians, some employers are more willing to flex work hours than others - depending on the workplace, the interest of the boss, and the runner's work ethic. But then, sometimes the person works a specific shift or has to open or close the shop. It is what it is.
"Life," John Lennon said, "is what happens to you while you're busy making other plans." There are things which are outside of the box of your control; traffic on the commute home from work, weather conditions, just to name two. There are things which you can plan for within reason, like school activities, religious observance (if you are so inclined), time for bonding with the family. And family, in my humble opinion, trumps (nearly) everything else, save for medical conditions. You, ideally, will be a runner for quite some time, but you will always be a parent, spouse, child, sibling. Your family members will be your first line of support in whatever you do, long after your coach or training partners have gone down the road.
Once the athlete can say how many hours they have available during the week to train, I can multiply by seven to give an "optimal" baseline number of miles/week. The optimal baseline, in my humble opinion, lets me recommend the longest distance the athlete should race as their goal event/s. I've been of the opinion runners can target three-to-six 5K races on a training volume of 25-to-30 miles a week. Training volume for two-to-three 10Ks per training cycle would be somewhere between 30-to-45 miles. Half-marathons or marathons would require anywhere "north" of 45 miles a week.
An important caveat: Just because a person has enough time to train for a race as long as a marathon does not mean they will have the physical ability to train for it. This is the dirty little secret many "Couch-to-Finish Line" programs don't enjoy speaking about. A friend of mine once coached a well-known program, and he saw too many first-year, really, just-off-the-couch, runners injure themselves during the program. I personally believe a runner should, if they are coming off the couch, race no longer than 10K during their first year. I wouldn't recommend anything longer than a half marathon until after at least two years of solid, consistent, injury-free training. It takes that long for the body to assimilate the stressors which come with run training.
So, what do I think needs to be part of a typical week of training?
Rest needs to be placed in the weekly training schedule, at least one day. There are some coaches who recommend a day of rest for every decade of life, starting with the 40s. So a guy like me who has been running for 16 years would probably benefit from 1-to-2 days of rest every week. I usually have at least a day or two days worth of cross-training during the week, but I listen to my body & sleep in or take a complete rest day when I'm feeling a little too beat-up.
Once a week, there should be a long run which takes up 20 percent of a runner's training mileage/time. Running coach Jack Daniels' recommends the long run to be no more than 2.5 hours, even as part of his marathon training protocols. I've always done my long run on Sunday morning, but some coaches, like Patrick McCrann of Marathon Nation, schedules his training plan long runs for Saturday, with a 40-minute run which focuses on skill & form for the next day.
I've tried the easy run on Sunday after a hard Saturday run & think it's pretty nice. That "kinder, gentler" run gives me a chance to run with less-experienced runners at a relaxed pace, socialize, & focus on my form.
During the middle of the week I schedule a "semi-long run" if training for half-marathon or marathon, or do a tempo run to work on race-day speed. This workout is usually sandwiched by a once-a-week speed workout which can be anything from fartlek, track repeats of 200, 300 or 400 meters at efforts ranging from just above aerobic to "See God" pace (that's a pace where if you took one more stride at that pace you would probably see God), or tempo run. The last piece I try to add works on strength. These can be hill repeats/bounding of 150, 200, or 300 yards at varied effort levels, or track repeats of 500-to-2400 meters.
There are important pieces of the training puzzle which need to be put into place, but you should first ask yourself honestly how big the puzzle can be before you begin to set the edges.