Articulate clearly, well-formed, elongated vowel sounds and clearly voiced consonants, so 'hello' becomes 'heellooo'
Use shorter sentences that are grammatically correct
Vary and raise pitch of voice (as much as an octave)
Stress words by pitch, intensity and length so 'sweet baby' becomes 'sweeet baybeee'
Use exaggerated facial expressions (eye contact, raised eyebrows, big smiles)
Frequently use repetition
Leave a gap/pause between sentences so that your child can coo and babble back (developing the turn taking structure of conversation)
Talk face to face so that they can clearly see how your lips move and other facial expressions (this about 20 cm or 8 inches for a new born).
Try using your child's name first then the important word in the sentence and follow with the complete sentence; for example, "Jo, bottle, here is your bottle!" Research suggests that at about 3- 4 months old a baby will turn their head when their name is called and that they will then focus on the next word that follows their name.