3. Tempo and Threshold Runs
No doubt you've heard about tempo runs and threshold runs, so I won't go into detail about them here. These types of runs work well for 5K training, but I like the fartlek and the progression run for the beginner because the change of pace teaches you that when you are uncomfortable, you can still run hard.
4. 5K Race Pace
I often refer to this type of workout as a "specificity" workout, and it's worth noting why: You need to train in a way that's specific to your event. If you're someone who has a goal of running eight-minute pace for a 5K, then that's just under 25 minutes. You will be well served to practice eight-minute pace in your training to break that 25-minute barrier. If you just go out and run every day and don't practice race pace, then you can't teach your body what that pace feels like—specifically, how it feels to run eight-minute pace and maintain it.
This is where the 400m track comes into play. Running race-pace workouts on the track will help you run specific paces because you get feedback every lap as you look at your watch to get that split. If you run four laps on a track and your goal is eight-minute pace, then you'll want to run for two minutes each lap. Obviously, some people think the track is boring, but if you want run faster, you need to view the track as a useful training tool.
A good 5K race-pace workout is 10 x 400m with a 200m float. That means you run 400m—one lap—at race pace, then you run a half lap "float" which allows you to recover, at a pace that is faster than a shuffle. So the float is slower than your easy day running pace, but not a shuffle (and definitely not a walk). At the end of that 200m float, you go right into your next 400m at race pace. This is a continuous workout and it's a great workout to do early in your training plan. The key is to start this workout conservatively; it's brutal if you run the first three or four 400m too fast, and then start slowing down the rest of the workout. No fun.