Letting a reader know who is speaking can be done in other ways. By using a character's action or reaction. Mary crossed toward him. "What are you doing here?" John scowled. "I don't get what you're talking about. Using these actions or reactions identifies the speaker and shows a bit of what they are doing.
Another thing some writers do is use adverbs to get across a bit of color to the person's speech. "I don't believe a word you've said,"Mary said haughtily. "Go away," he said glumly.This is all right but showing is more effective. Mary's eyes iced. "I don't believe a word you said." His lips turned down and he lowered his eyes. "Go away."
Another thing is avoid are soliloquities. This is where a person goes on and on making the dialogue into a paragraph or more." What happens here is the reader forgets what the character is talking about. Break these long bits apart with some kindof action or reaction by the listener.
Now a word about dialect. Use this sparingly. I once read a book by a favorite author that I put aside because the characters were so heavily into dialect that I had to stop and puzzle the meaning of every conversation.
Next week, I'll give a check list for you to use when revising the dialogue in your story.