Find the best possible order to combine enchantments in order to spend the fewest possible levels when combining books.
The most efficient way to enchant is to get exactly enough levels for each step. If you take this approach, select the setting to optimize xp.
If you intend to add more enchantments to the item later or repair it with an anvil, then select the repair cost option.
Finally, if you are renaming the item, do it on any step of the process that costs the fewest levels.