1. MOTIVATION:  Getting started is important for beginners; keeping going is a necessity for even experienced runners. A good coach can provide the necessary jump-start in the first case and continuous pushing in the latter. Reporting on a regular basis to a coach/mentor--even only once weekly or by mail or phone--can provide an important keystone to any training plan. "Your `average' athletes aren't as highly motivated as Olympians," explains Robert Vaughan. "They work 9-to-5 jobs and can't be expected to train twice daily, or get a massage four times a week. But given their limited time, a good coach still can motivate them to achieve their best."
2. SYSTEM:  "Good coaches are like chefs," claims Gary Goettelmann, a coach in Santa Clara, California. "They have a methodology and a system. A disciplined athlete who follows his coach's system is bound to improve." Often, the details in any system are secondary to its mere existence. Jack Daniels claims you could use eight different systems to train the same athlete and achieve the same results. He says, "Having confidence in the system is more important than the actual system itself."
3. PLANNING:  "Proper planning can help sharpen a person's goals," says Atlanta's Mary Reed. "A person who would like to break 40 minutes for 10-K and three hours for a marathon may fail at both goals because they're too diverse." A coach can help pick goals that are realistic and design training plans to achieve those goals, both long- and short-term." Goettelmann adds: "This frees the athlete to concentrate on the activity rather than the planning of it. That provides better focus."
4. ADVICE:  Once a runner has been working for several years with a coach, the training plan becomes obvious: long runs on Sunday, intervals on Wednesday, rest Friday before the race. But even dedicated runners need advice. Benji Durden worked with 2:26 marathoner Kim Jones for nearly a decade. "I don't do as much coaching as I did at beginning," says Durden. "I've gone from being a coach to being an adviser. Kim developed to the point where she didn't rely on me for every decision." Jones concurs, adding: "Every athlete needs someone there to guide them with those decisions." One key role for coaches advising elite athletes is that of picking races, particularly knowing when to say no in this era of run for the money. But average athletes need similar help to avoid over-racing.
5. INJURY PREVENTION:  A coach who carefully monitors an athlete's progress can recognize when the athlete begins to show signs of the fatigue from overtraining that often precedes any injury. A coach standing beside the track during a hard interval workout can call halt, whereas an uncoached athlete might plunge ahead. If and when injuries do occur, a coach can chart a course of rehabilitation and call upon the best medical advice to affect a cure. According to John Babington: "A coach's most important role may be preventing overtraining, which leads to injury, which puts you out of commission."
6. PLATEAU BUSTING:  Sooner or later, all runners reach the point when they fail to improve. How to get off a plateau is a common problem. "When I was self-coached, I felt I got stuck at one level," says Lynn Jennings. "I had accomplished all I could do alone." Jennings' first world championship in cross-country came after she began working again with Babington. The same advantage is available to average runners who find a coach. "New runners only do what's fun," explains Reed. "If speed is fun, they train only on the track. If distance is fun, they never do any speed work." A good coach can suggest different types of training that may allow the plateaued runner to climb upward to a new level of performance.
7. CHECK LIST:  A good coach keeps an athlete on course by making certain the athlete follows the system and plan, as above. According to David Martin: "A coach who is doing his job remembers where the athlete is heading. He will have a check list of what's important about different phases of the training plan. So when it comes time to do a specific workout, the coach can remind the athlete what they are trying to achieve. This frees the athlete to concentrate on the actual training itself."
8. FEEDBACK:  Most runners have a hard time evaluating their own training. Keeping a diary helps, but still is no substitute for a good coach. "Runners tend to doubt their training," confesses Jennings. "If they are worried that they haven't quite done enough they think, `Gee, I better do more.' Having a coach circumvents that, because a coach is an unbiased observer. A coach can look at your workload and evaluate it more objectively than the athlete. That's positive, because a coach can say your mileage looks pretty high, time to do faster work. Or too much speed, you need more of a mileage base."
9. CHEERLEADER:  Runners' muscles run on glycogen, but their minds often run on praise. They need encouragement. According to Gordon Bakoulis: "A coach can be emotionally helpful particularly when you have a bad race. The coach can offer a pat on the back, for starters, then later after you've digested your disappointment, the two of you can sit down and analyze: why the bad race?" She adds with a smile: "When you've had a good race, it's also nice to have someone to celebrate with."
10. FUN:  Finally, a coach can make training fun by varying what the athlete does--even where they run. The coaching environment offers an opportunity to interact with other runners working with that same coach. "Athletes do need coaches," says David Martin, "but how do you define athlete? Even the everyday jogger, whose only goal is to have fun, can benefit from a coach." For those who run for enjoyment, that may be the best reason to seek coaching help.

Taken from the Road Runners Club of America website