By about 3 years of age, most of your close family should be able to understand what your child is saying. If this milestone has not been kept, it is best to contact a speech and language therapist for an assessment. However, there are things that you can do meanwhile at home to help build your child's speech clarity:
1) Avoid using a pacifier/ dummy. Prolonged dummy use, especially when a toddler is just learning to speak, can get in the way of speech development. It can lead to multiple speech errors. If your child is fussy and using a dummy makes your life easier, then use it sparingly - preferably, only at nap times.
Different types of pacifiers are available in the market. Use these sparingly.
2) Move your child to solids (about 6 months) and lumpy solids ( about 9 months) at the right times. Keeping your baby/toddler on a semi-solid diet for too long can deprive the tongue and mouth of movement and sensations it needs to learn and this can sometimes delay speech development. Even if your child is a fussy eater, avoid blending foods in the mixie beyond the 9-10 month stage; certainly not after 1 year.
3) Spend time talking to your child and playing with your child. Speech is a skill and like with any other skill, it becomes better with practice. If your child is mostly left alone or with gadgets, he will not get the speech practice that he needs. This could lead to speech and language delays.
4) When your child makes a speech error, show him what's correct by repeating it back for him. So if your child says, 'Look! There's a tar!' say again for him, 'Yes! There's a car!' Avoid correcting him. Also avoid asking him to repeat words after you. For a child who finds this difficult, it will just be a frustrating experience, and therefore best avoided.
5) Don't pretend to understand your child when you actually don't! Sometimes it might seem easy to just pretend to understand. The problem is that your child will continue believing how he says a word, is the right way to say it. Instead, gently tell your child 'I don't know what you're talking about. Can you show me please?'
6) Remember that if your child has significant speech clarity issues beyond 3 years of age, it is time to seek the opinion of a speech and language therapist.