My first question to you is “When did you last go through a base phase?”. Your base training will make your race day a faster, more comfortable and efficient experience. The greatest improvements in your race day performance come by increasing your aerobic capacity. This is why it is important to truly build a strong base before you do any specific training sets. As your specific endurance workouts progress, any details you glossed over in your build-up will become evident as you start to get more specific. However, it is incredibly challenging to back-track once you are doing sets without a solid base! If this is the case, try a “run slower to get faster approach”, and go back to base training. Your weekly mileage may be lower at first, but the aerobic benefit you’ll receive will outweigh this perceived loss.
From zero to hero
The secret is that progression is everything in these workouts. Use this mentality to help teach yourself to negative split (have a faster second half than first half). Remember, we race how we train - so practice this. Train on terrain that simulates your race conditions, even if those conditions don’t allow you to perfectly hit pace in your workouts. Get specific!