Copy/Paste into "Main Options" -> "Import/Export/Restore" -> "Import from String"
This will display an icon in the middle of your screen that recommends the best skill/spell to use for Frost DK priority. It determines which spell to use based on duration of dots on target, your current runic power to prevent capping, spending runes ASAP when they come back from CD, and HP of target for execute phase to optimize DPS.