Use the right material in the anvil
Combine enchanted books before applying them
Rename items before repair costs get too high
Avoid repeated anvil repairs on the same item
Use Mending to repair with experience
Use Unbreaking to reduce durability loss
Make a fresh copy of the item if repair cost is too high
Use grindstone to remove unwanted enchantments
Keep high-value enchantments and avoid adding unnecessary ones
Repair items with the same base item instead of mixing methods