Here’s a tip for writing a great character: cross out their name.

See this script page from Breaking Bad? I crossed out the names of Walter White and Jesse Pinkman. Identities erased. Now, read the page and guess which lines are Walter’s, and which are Jesse’s. I bet you get a 10/10, first try.

Why is that? The writer probably knew every line of dialogue was an opportunity to reaffirm, sharpen, and individualize a character. String enough of those lines together, and you'll start to witness a unique human being rise off the page. That's magic.