Generally I talk about specific workouts in this space but today I'll talk about some more general tactics that you can use across all your tempo runs to make improvements in those workouts and by extension your general fitness and racing. For me I put all steady running faster than regular training and longer than a mile or two into the category of tempo training. This could be something as short and fast as 2 miles at 5k pace or as long and slow as 27 miles at 80% of your goal marathon pace. All are designed to improve your aerobic fitness, though in many different ways, and all can be improved using some of the same tactics.
To me the most important thing about a tempo run in training, really any workout in training, is not how you run it the first time but how you run it better each successive time. Good running is after all in its simplest state all about getting better.
I have done a ton of work over the years and one thing I have seen in my running and others again and again is if you take your tempo run and just try and run it faster each time out at first you are able to do so but in general you are not running it better you are just running it harder and soon enough you are running as hard as you can and your not going much faster. In short you stagnate.
The key is to instead increase distance at the SAME PACE. So you go out and do a 3 mile tempo run at 5:30 per mile. The next time out you should aim for 4 miles on the same course at the same pace. You will find that you are able to fairly quickly find yourself running twice the distance at the same pace and your effort when going by the original distance is much lower than when you started.
After you have increased the distance a good bit say 50% to 100% longer than the original distance than you go back to the original distance and run it faster. You will find the effort is not increased. In fact often it is less. Through cycles like this you can make very big gains and make them very consistently.
However sometimes you will still stagnate. In these cases there is one more trick to try. In this case you run a fast finish. So at one point I was trying to build up to an 8k to 10k tempo run on the track at 3:00 per K. Thing was I was stuck at 5k to 6k. I built up to that well. I was doing some other work but I was stuck. So what to do? I ran an 8k tempo run where I ran slower than I had been for the first 5k, in my case 16:00 so 3:12 per k. That is about 5 to 10% slower than goal pace and then I finished at or faster than my goal tempo pace, in this case I ran the last 3k in around 8:50. So 2% or 3% faster than pace. Even if it is dead on pace that is ok.
The results? Next time out I ran 8k in 23:56. It isn't a sure fire thing but sometimes the reason you are stuck is you really lack the endurance to run the later part of the run at that past and this can specifically target that weakness.
Finally sometimes the answer lies outside the specific workout. If these two tricks don't work and you are still stuck it is time to work on other types of workouts to build up your abilities around your tempo run. Most often either intervals at your tempo pace or 5% faster for the volume you wish to run for your tempo or as much as 50% more volume this can improve the muscular endurance and efficiency. Second is to run a longer tempo at a slower pace to build the aerobic endurance and efficiency.
Hopefully you can use this to get the most out of your tempo runs and reap the improvements you deserve for your hard work!