I have two children, and they are very different from one another.
My daughter spoke full sentences at 1 year old. She used large words, very mature for her age.
My son knew what he wanted to say and was very intelligent, but he couldn't pronounce the words. He was diagnosed with phonological disorder.
These are some things I did.
1) I played classical music on CDs throughout each pregnancy.
2) I talked to my children and read stories at bedtime during my pregnancy to set up good routine for when they were born.
3) I purchased many books and started a library for my children.
4) After my children were born, I read to them every day. I stayed home with them. I spoke clearly to them as if they were other adults. I never used baby talk or baby babble.
5) I often praised my children. I never used derogatory words or insulted by children.
6) I addressed my children to use their words if they needed something from me, instead of acknowledging their pointing (like babies some time do and grunt for something) or talking for them. I never spoke for my children, I always encouraged them to tell me what they needed even if I knew, because I wanted to strengthen their communication skills.
7) I spoke slowly to them instead of rushing through words expecting them to understand me without becoming frustrated.
8) I set up chalkboard walls in my home and created an art center so they could use their creative imaginations. My children had many toys. I converted the basement in to a play room and invited friends over often. We also hung out at the park with other children as much as possible.
When they were in pre-k, I enrolled them in school. Because my public school had a lottery and could only pick one of my children, I enrolled them in private school.
I ended up homeschooling when my son was diagnosed with Autism so that I could take him to all of the necessary medical appointments and care for him round the clock. I took him to the best hospitals in Boston for speech evaluations and then enrolled him in a local one where I had to take him 2 x a week for 6 months. Then, I enrolled him in public school when I felt he was able to learn without having constant meltdowns and being disruptive to the other students or teacher.
My children are both avid readers. My son speaks fluently in English and Spanish now even though he still needs speech therapy for parts of his disorder.