Here’s a worthy bit of advice–only use speaker tags when needed. Too many writers feel they have to put “he said” (or worse: “he quipped, interjected, exclaimed”) every time any character says something. However, most of the time the reader knows who is speaking. If you are writing a conversation with just two people, you only occasionally need to mention the speaker’s name just to keep the reader clear. But alternating with a narrative tag instead is a good idea. Don’t use both.
John shook his head. “I wouldn’t do that if I were you,” he said.
John shook his head. “I wouldn’t do that if I were you.”
Be sure that when you do use an action (narrative tag) to identify who is speaking, you keep the action and speech together in the same paragraph to avoid confusion. Too often in the manuscripts I edit, I get confused as to who is speaking because the writer will put a line of speech on one line, and then that character’s action in the next paragraph along with a different character’s speech.
And it always sounds more natural to say “John said” rather than “said John.”