The success of getting a connecting room pair begins with the physical configuration of the hotel.

Some hotels were built with few if any connecting rooms, while others have way too many (at least for those of who don't like a connecting door, when we're only getting one hotel room).

Another issue is what types of rooms connect at a particular property. King-to-king? King-to-double-double? Double-double-to-double-double?

As this thread indicates, the word "connecting" is unambiguous, while the word "adjoining" is best avoided because it means different things to different people.

I would recommend calling the hotel well ahead of time to get the hotel's advice for how to get a connecting room pair successfully, with the right kind of beds in each room.

Back when we were getting a connecting room pair for family vacations, some hotels blocked me into a room pair months ahead of time (and kept their promise), while other hotels read the line to me, "connecting rooms are never guaranteed."