Prepare for fasts by getting keto adapted, last few days before fast should be very low carb, moderate protein, high fat. If you’re doing back to back fasts, eat like this in-between.
Very important to not go off the rails when not fasting and maintain low insulin. If you have to eat carbs for some legitimate reason (I don’t think there are any), look into metformin or berberine (not medical advice).
Also it just gets easier the more you do it. Especially if you don’t screw up during the non-fasting time.
Also electrolytes.