Every writer is exhorted to 'find their voice'. Don't imitate anyone else, we are told, write like you.
Okay, this makes sense. I am able to write with other writers' rhythms (I've got one mystery game that is very Jane Austen...on purpose), but it's easiest to write like me.
But never forget, each of our characters must have their own voice as well. Not ours; theirs.
Each character is in your manuscript for a reason. (if there isn't a reason, then maybe you should rethink them - but that's a whole different post). Give them their own voice. Their own rhythm. Their own vocabulary.
I've found this a wonderful tool for enabling each character to stand out beyond any description of their physical appearance or habits. I have one character who speaks in very short sentences. Another who has a rather dry sense of humour. One who is terrified of making a social faux pas and therefore picks his words with extreme care.
The better you know your characters the clearer their voice becomes. What is their level of education? Where did they grow up? What's the level of their self-esteem? The latter is very useful when it comes to vocabulary choices. A confident character will say what they wish; a less confident character will try to please. Some characters will take joy in shocking others and their language will reflect this. Do you have a character where English is their second language and if so, how fluent are they? Don't take the obvious road, it could be fun if this character actually has a better vocabulary than some others. Confound the stereotype.
Take a look at whatever project you're working on right now and just look at the dialogue. Can you instantly tell which character is talking? More importantly; could someone else?
Remember: although all these characters sprang from your brain, they're not you. Give them their own voice.