Here is a good tip I found out about recently:
Boil eggs, then cool. Place cooked egg yolks in a ziplock bag and seal. Mash yolks well and then add the remaining ingredients, seal, and mash until mixed thoroughly. Cut off the tip of one corner of the bag. Squeeze mixture into eggs. Throw away the bag for easy clean-up.
Great tip…so simple and yet never thought of it!