This is the most important step for main and semi-main characters.
Give them a vocal tick when speaking.
Many of the most memorable characters of all time have these and it makes them easy to identify in a long string of dialogue.
A good example is Yoda who inverts grammar structures.
But you don’t need to be that complicated. You can have them address people in a slightly odd way or even just a special way of addressing your main character.
Have a go you’ll be amazed how much life it brings onto the page.
