​​As my high school English teacher always said – Keep it super simple! 

Directly from Wikipedia: 

The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore, simplicity should be a key goal, and unnecessary complexity should be avoided.

Application: 

Keep your language simple.  If your child is only speaking in 1-4 word phrases, keep your sentences around this length as well.  Any longer sentences may be confusing and your child will start to tune you out.

Remember to get down to your child’s eye level and gain attention before giving instructions.