This is a question about Programming which can be a big hairy can of worms. But to try to answer, I'd suggest trying to increase your target speeds (using the technique mentioned above) for each effort, even if that means more recovery, which might mean cutting out the last planned effort of the day. Maybe recover based on perceived heart rate. Basically, when your heart rate returns to somewhat normal, it's time to go again.
What should I look at increasing first? The amount of times I do certain workouts or the amount of times I repeat whatever the distance is in a given workout??