What is your most successful program design for a half marathon?

I don’t have one particular plan to refer you to. I create plans for my clients tailoring it to their schedule and needs. Here are some important things in a plan. One long run each week: this gradually increases each week depending on where you started from, but every 3 weeks, have a cut back week with less mileage. For a half, you don’t need to run more than 4x/wk. The other runs throughout the week are shorter and easier. If you’ve done a half-marathon before and want to increase your racing time, then doing speedwork (intervals, tempo runs, etc) one day a week is good. But if it’s your first half-marathon, then don’t focus on speed, just focus on endurance. Make sure you give yourself rest days. Find a good coach who can create a plan for you, then follow the plan! Good luck!