Almost every runner plateaus from time to time. Often the best cure for this is a training adjustment. Sometimes, even a slight tweak will result in faster times, but just as often, the whole training program needs to be overhauled. Whether you are just looking for some new ideas, or you are thinking that your training regimen needs drastic modifications, check out the suggestions below for ideas of techniques you may want to consider. Incorporate one or all and watch your time drop.
1. Rest more. Sometimes we get so caught up in training and striving for that lower PR, that we forget that one of the most critical facets of training is, in fact, rest. Your body doesn't get stronger, more capable of faster times, during actual running - or cross-training for that matter - but rather, during recovery/rest. For two weeks, try taking a complete rest day on one of the days that would normally be an easy training day, and make an easy day out of one of your hard days. And be careful not to make your other training days more intense to compensate. That would defeat the purpose of the added rest. This will give your body a bit of extra recovery. Then return to your usual training regimen. If you are sluggish and not seeing the kind of results you want or expect, taking just one extra day off might make the difference, but if it doesn't, try my two-week plan.

2. Hills. If you are not already doing regular hill training, try doing some, but only do it once a week, and do it on one of your hard days. If you already have two hard days per week (not including your long run), then replace one of them with a 'hill' day or reduce the rest of the workout to make room for some hill training. There are many types of hill workouts. Just google "hill training running," and you'll get plenty of ideas, but be sure to start gradually with only a small amount the first week. If you are saying to yourself, "We don't have hills in Tampa," I have two suggestions: The closest hills are near St. Leo College in San Antonio. Most serious runners travel up there to do their hill training. It's about 45 min. from downtown Tampa. A more convenient second alternative is the overpass on the Upper Tampa Bay Trail. You can do repeats on that without worrying about vehicular traffic. A third alternative is to train in a parking garage. Make sure you do this when there are no cars to compete with. The last alternative would be a treadmill, but this is not nearly as good because you can't go downhill, which is also important.
3. Spin. If you are not spinning already, add one spinning workout per week. By this I mean a spinning class. Do this on one of your hard days; otherwise it will not help and might hinder because your legs will never get to recover due to spinning being an intense workout. I recommend spinning after your run on one of your hard weekday workouts, but you could also do it first. Another idea is to do it instead of one of your hard workouts. Maybe alternate with replacing track work with spinning one week and replacing tempo with spinning the next week. Spinning will increase your leg turnover speed and your leg strength, but it has many other benefits as well.
4. Leg turnover drills probably have the greatest potential for increasing your speed. These are sometimes called foot strike drills. See how many foot strikes you can do in a minute. Strive for about 90, counting only one foot or 180 if you count both feet. Don't pay any attention to forward movement. That's irrelevant. Just concentrate on rapid foot strikes. Cool down with an easy jog for a few minutes. Then repeat. Great drill.
5. Drills. There are many different kinds of running drills. The purpose of most drills is to overemphasize correct running form. Every running coach has their favorites. Go to YouTube and enter "running drills" or "drills for runners." Don't just accept anything you see; look for drills demonstrated and recommended by well known, credentialed coaches.
6. Add weight training. If you've never done any weight training, you might be very surprised at how much it can improve your running speed. AND don't ignore your arms. They are the levers that help you propel the legs forward. If you are already doing weight training, consider making some changes in your workout; be sure you are doing the right exercises for runners; you want to strengthen all muscles, but remember that there are usually several ways to strengthen each muscle group, and some will be better for runners than others. And be sure you are performing them correctly. 7. Core. Improving core strength helps you to be lighter on your feet. It will help you avoid sinking into the ground with each stride; rather you'll feel more like you're gliding over it, which is, of course, faster. Study photos of yourself when at the end of a race. You may notice that you look like your torso drops closer to the ground with each stride than it did in photos taken early in a race. Strengthening your core and all other muscles will help reduce this type of fatigue and keep you running with less sinking.
8. Lose weight. Many runners can afford to lose a few pounds. Even a few pounds will make a difference in your speed and comfort. To investigate this, put 10 lbs of weight in a backpack and go for a run. Nothing will convince you more effectively.
9. Try some plyometric exercises. Be very careful here because these can easily get you injured and will always get you sore, at least at first. Make sure you do each exercise correctly and do them on a hard training day. Basically, plyometric exercises are explosive exercises. Google "plyometric exercises running." You'll find plenty of videos on YouTube, but be very careful, and don't do this if you are not already in peak condition. Even then, start with only one or two reps of only a couple of different ones each week, and build from there. And, of course, you don't want to even experiment within a couple of weeks of a race. Better to incorporate this in your next base phase.
10. Run off road on rugged terrain at least once a week. Running through sand, hopping over roots and adjusting to varying uneven ground will require much more mental concentration, but it will also strengthen your ankles, require more balance, and increase overall agility. As a result, when you run on pavement it will seem easier, and you will be stronger. An added benefit is that it is less stressful in other ways due to the fact that it is on soft surface. Therefore, it will be easier on your body in that way.
11. Increase your base miles. Many people try to race and set new PR's after not completing an adequate macro cycle. In other words, they don't spend enough weeks going through the necessary training phases before goal races. If you are striving for a PR in a particular race, you need to carefully prepare for months in advance. Of course, the length of the preparation period/macro cycle depends on the distance of the race you're preparing for. Even if your goal race is a 5k, you will have a much better performance if you started your training/preparation for that race by building a base of at least 20 miles per week. If you are training for a goal 5k and don't plan on racing any longer distances, I still recommend building your once weekly long run to at least 9 miles and building to 25 miles per week. If you have not done this in the past, you may find that it is the secret to having a breakthrough race.
12. Eat more protein. Of course, your whole diet is important, but I have particularly found that many athletes do not get sufficient protein for the quantity of training they do. I suggest keeping track of your protein intake for a few days. It may be that your muscles cannot get stronger and can't recover properly because you are not consuming enough protein. I recommend listening to some podcasts about nutrition for athletes. A highly recognized national authority on nutrition for athletes is Nancy Clark, MS, RD, CSSD http://www.nancyclarkrd.com/index.html. It could be that all you need to achieve a better time is a better diet.
13. Take a long, hard look at your running schedule. Does it make sense? It is carefully planned or haphazard? Is your training specific to what you need for the events you normally compete in?
14. Avoid any intense training sessions the week of any goal race. By that I mean a race in which you hope to set a PR. The only hard training you should do during that week is race specific but that should be minimal because you need to be very rested for the race.
15. Take a weekly yoga class. This is an excellent way to improve core strength, increase balance, and improve flexibility.
As always, be careful not to overtrain, i.e., work too hard too often, and don't do anything you are not properly conditioned to do. Keep in mind your age, experience, and current fitness level. Also, you wouldn't want to try to incorporate all of the ideas at once. Consider where you are in your training cycle before adding some of these ideas. If you are in the middle of your racing season, it may be best to wait until after the season and incorporate some of these ideas into your next macro cycle.
After reading this list, you may be pumped to try a few, but one caveat, if you did not begin the season - your macro cycle - by building a sufficient base, then that is the most important thing to change. First, because it is the most likely thing to result in improvement, and, second, because doing so will greatly decrease the likelihood of injury, allowing you to safely incorporate the other suggestions.