1) Hydrate! Drink enough water everyday until your pee is a pale yellow/almost clear. If you are already dehydrated you won't be able to catch up in the few hours before the workout. Sweat releases electrolytes, so consider adding an electrolyte supplement to your water to ensure your muscles can provide peak performance during your WOD.
2) Increase your STARCHY carb intake! For the extreme energy output required to smash an open workout, you need to ensure your glycogen stores are full. Increase your intake of slow digesting carbs in the days leading up the workout to ensure that you are adequately recovered and glycogen stores are full. If it is a short WOD and your body doesn't have time to tap into stored glycogen, ensure you have glucose in your bloodstream by consuming slow digesting carbs like sweet potato or brown rice 3-4hrs before you do the WOD and/or quick digesting carbs 1-2hrs before the WOD.
3) QUALITY Sleep! Aim for at least 7-9hrs of sleep to ensure you are fully recovered and energized to workout. If you lead a stressful life or have difficulty sleeping try a supplement like Paleoethics Recovery Matrix . The combination of magnesium, collagen, zinc and other amazing anti inflammatory ingredients improve the quality of your sleep, while helping your body heal simultaneously. Win-win!