It is good to have a visual of the alphabet for children to refer to when they are working on problems pertaining to alphabetical order. This visual can be on a standard sized paper that lists the alphabet in order or alphabet cards that are posted on a wall.
Alphabet cards are a great resource for children to have when they are putting words in alphabetical order. They can lay the cards out in order and refer to them as needed. Then when they are done, they can just put them away.
Play an alphabetical order game with your child for practice. Find a few objects from around the house and have your child put them in alphabetical order.
The dictionary gives children good practice with alphabetical order. Tell your child that you are timing how fast they can find a word in the dictionary and make it a game.
Some alphabetical order problems tend to get more complex when they have the same beginning 2-3 letters. Talk to your child about strategies they can use to help them organize their thinking. Underlining letters that they are comparing, rewriting words on a different piece of paper, etc.