When we read dialogue, we should be able to distinguish between each character even without tag lines, simply by the way they speak: the cadence, the word choices, pet phrases, etc.
You can discover these kinds of individual dialogue markers by listening carefully to the people around you. Are there particular words or phrases a certain person favors? Does she speak in cliches? Does he use similes to illustrate is point? Does her voice get higher when she gets excited? Does he pause between words?
In addition, pay attention to the physical gestures that accompany speech, such as neck scratching, eye rubbing, ear tugging, etc. These gestures can help suggest the attitude or emotional state of the speaker. They also provide visual cues to help the reader "see" the characters while they are speaking.
Dialect is dialogue that is spoken either with a foreign or regional accent. Be careful, though, not to overwhelm your readers with pages of phonetically spelled dialogue or whole speeches made in a foreign language with no translation. Generally, a few key words or phrases are enough to tune the reader''s "ear" to the dialect.
Writing dialect is a skill to be practiced and it begins with careful listening. If you want to imitate the dialect of someone you know, listen carefully for the words they use, their pronunciation and sentence structure. Pick one or two distinctive characteristics to use in your passages. If you don''t know anyone with the accent you need, rent a video. Just make sure you pick a serious film that was well received by the critics.
Learn more about the Fundamentals of Fiction Writing Workshop.