Practice, Practice, Practice. Even 5-10 minutes per day can make a huge difference! See your Speech Language Pathologist for lists of words appropriate for your child.
Be a good listener. Listen to what your child is trying to say, not how it is said.
Ignore mistakes. Use correct speech that your child can imitate. Don't imitate the wrong way they are saying it.
Help your child focus on sound patterns of words such as those found in rhyming games

Talk with your child frequently
Ask and answer questions about things happening in their environment.
Read to your child. Read a variety of books. Ask questions about the story.
Talk about what you are doing. (cooking dinner, washing dishes, bath time, cleaning, etc.)
Give directions for your child to follow (e.g., making cookies)
Expand what the child is saying by adding a little more information. If the child says "car go" you could say "see the car go".
Wait! Give your child time to respond to your utterances.
Talk about how things are alike and different.
Give your child reasons and opportunities to write.
Sing songs.
Teach your child Nursery Rhymes.

From "7 Tips for talking with your child" - The Stuttering Foundation
1. Reduce the pace. Speak with your child in an unhurried way, pausing frequently. Wait a few seconds after your child finishes before you begin to speak. Your own easy, relaxed speech will be far more effective than any advice such as “slow down” or “try it again slowly.
2. Full listening. Try to increase those times that you give your child your undivided attention and are really listening. This does not mean dropping everything every time she speaks.
3. Asking questions. Asking questions is a normal part of life – but try to resist asking one after the other. Sometimes it is more helpful to comment on what your child has said and wait.
4. Turn taking. Help all members of the family take turns talking and listening. Children find it much easier to talk when there are fewer interruptions.
5. Building confidence. Use descriptive praise to build confidence. An example would be “I like the way you picked up your toys. You’re so helpful,” instead of “that’s great.” Praise strengths unrelated to talking as well such as athletic skills, being organized, independent, or careful.
6. Special times. Set aside a few minutes at a regular time each day when you can give your undivided attention to your child. This quiet calm time – no TV, iPad or phones - can be a confidence builder for young children. As little as five minutes a day can make a difference.
7. Normal rules apply. Discipline the child who stutters just as you do your other children and just as you would if he didn’t stutter.