Different career choices bring certain words to a dialogue. Medical people choose words the average person might not. Cops have a distinct vocabulary. So when you're writing two people talking think of who they are, and what they are.
Men and women tend to speak differently. Women often use longer sentences and men shorter ones. This isn't always the case but be aware when you're doing dialogues.
Some characters use flowing sentences. They almost sound like poets. Others use terse remarks. Also what is happening will add to the tempo of a sentence. Danger can cause terseness. Making love can evoke longer sentences. Dialogue is a good wat to show what the person is feeling.
Tone is part of dialogue and can be difficult. Sure adding an adverb like seh said lightly. He asked angrily. These give the idea but sometimes when writing dialogue putting those adverbs in can be intrusive. This can be done by putting a bit of action. For example "What are you doing here?" Mary asked angrily. or What are you doing here?" Mary's hands fisted on her hips. Both set a tone but the second one brings the reader's imagination into the story.
There will be something next week on how to use dialogue in your story.