Always read to your child throughout the day, every day, which you probably already do, and always run closed captioning whenever your child is watching tv or a video! Our youngest was spontaneously reading just before her third birthday, yet she didn't even start speaking in complex sentences until just a few months prior to reading. She's just turned five and we still run closed captioning (we started using closed captioning upon the recommendation of an audiologist when she was 6 months old)...we know that she is actively reading along with the dialogue because we can mute the sound and she rarely complains, and she can discuss the storyline with us. And with her over excitabilities, she finds movies less scary because she can't hear the sound effects and mood music if she is "reading" the program she is watching.
I am always surprised how different a reader DD is throughout the day. In the morning she might breeze through sentences, in the afternoon she gets hung up on "cat", and it is never consistent. Some days she is better in the mornings. Some days she is better in the evenings. Occasionally, I will think she is way too tired to read at night, and then she reads an entire book without any hiccup.
Also, Reading the TV on mute is lovely. I am very visual-spacial, and love closed captioning. Perhaps I have some auditory processing issues because I have a really hard time understanding people sometimes. CC is great for that. I wish I had it in real life. I actually used to be a linguist. Part of my job was transcribing what people said, and not only was this in Arabic, but they were usually speaking in some kind of code on top of accents, and the audio was muffled. I guess I loved the challenge, but I still find myself using some of the skills I learned back then just talking on the phone with a stranger or speaking to someone with an accent. (like rewinding the audio in my head, and visualizing the words.)