Dialogue is a wonderful thing. Most good novels have a hefty chunk of dialogue, often making up a third of the text or more. Conversation allows for subjective viewpoints from characters to be conveyed. How they speak, whether they have an accent and the composition of sentence structure within speech can all convey personality. Education, ethnicity, even class.
"I'd like to take the dog for a walk." It's boring but neutral.
"Get that mangy mutt outta ma house!" Could suggest a lack of education, or a country dweller.
"One would like to take the corgis for a stroll around Balmoral." All right, this is a cheap impersonation of the Queen, but you get my point.
What is being said, when and how are a great way of showing rather than telling. Impatience, anger, sadness and regret can all be very effectively laced into a conversation. But if you've got an 80,000 word manuscript and a dozen or more characters then it's easy to slip into your own voice.
This is where colour coding your manuscript comes in. Keep all speech in a highlighted background colour for each character. For us that might be yellow for David Morton, green for Edwin etc.
At the end of the first draft, copy paste all the speech from each character onto a clean page. Then you can ensure that every line is semantically consistent. Speech is often peppered with habits, favourite phrases and associated gesticulation. If you can convey that consistently, you get a great depth to the character. One word of caution here - don't overdo accents. Readers will find it hard to follow if you've got an unusual accent, or plain irritating. Anything excessive is probably best kept to minor characters.