Each switch of a speaker in a dialog is it's own seperate paragraph.   Alice should never say anything in the same conversation as Bob, and vice versa.   Keeping the speakers paragraph seperated helps the reader parse who's side of the conversation it is.   For dialog between two people, so long as the order is preserved, you need not repeat the said tag, though having the characters other actions contained in the paragraph is fine.  If there are three or more, it becomes prudent to tag who is speaking in each new paragraph as order is not as easy to preserve, though if Character A and B start to have a coversation with each other and C stops speaking to listen, order is preserved until C resumes his part in the conversation.

> "I said this," C said.
> 
> "Well, I said that!" A said.
>
> "A," B interupted, "What did you say?"
>
> "That!"
> 
> "Oh!"
> 
> "Can we get back on track?" C asked

Notice that B and A have quick dialog between them where A answers B and B reacts.  No tags are used because it's implied by the two paragraphs on either side that A will respond to B's question, and the second tagless dialog can't be A (he just spoke) or C (he's tagged in the following paragraph).

If the quoted text needs paragraph breaks (A is going on a monolog) then the paragraph should at most note he's continuing, but but is not part of the same quote sandwhich (i.e. Paragraph one should end with a closed quote and paragraph two should begin with an opened quote.   It could be that A is going to do some non-spoken actions.).

Remember, dialog is an action and all of one character's actions in one instance should be contained to one paragraph.  A character can speak and jump, but cannot speak, jump, summersault, speak, pour a drink, speak, speak, eat a hamburger, and speak in one instance.