Character names in dialogue

You should either choose one, or interchange them based upon the situation.

For example, a superhero script, would have the same character sometimes listed by their superhero identity, and sometimes by their real name. This isn't always a hidden identity, for instance in the X-men movies. There are times just based on his presence and actions when Wolverine is listed as Wolverine, and sometimes Logan.

If your character is going to have times when he is in a military situation, and times not, I would suggest calling him by Rank and Last name when in the military enviroment, and by first name when he is not.

If it is a consistent enviroment (war story or such), it would depend on the character. If it is the main character, i'd list him by his first name for the most part. A supporting character it would be better to list them by their rank and last name, Especially if they are superior officers.

Your question

is a two parter.

1, Technically there is no rule against a full name being placed over dialog.
Likewise there is no rule against a nickname or just the first name.
However you wouldn't really want to place John Jacob Jingle Himmer Schmidt over a character's dialog.

The basic rule is clarity. Make sure everyone can clearly identify who is delivering the line or doing the action, so....

part 2. You want the dialog name to always be the same throughout the entire script. If you intro him as JOHN SCHMIDT then his name should be John Schmidt every time he has dialog. It is perfectly fine for another character to call him John Jingle, or Schmidt, or Jacob, or JJ, as long as it is CLEAR who they are talking about. BUT if you switched to one of these then it would become confusing.
Screenwriting people are trained from the get go that an all capped name means two things A new character or B dialog is coming.
If they see a different name over dialog they will wonder why this new character hasn't been intro'd properly.
It is acceptable to shorten the character name to just the first name for action lines.
This is one of the reasons it is best to have varity in your character names.
Mary and Marie, John and James, etc, etc are too similar.

When in doubt go for clarity.

[Just read Kap's post. The Wolverine/Logan example is excellent, for split identities. In that situation it is very clear that they are the same person but the character name signifies a different side or personality.
That doesn't really work if you are dealing with ordinary folks.]

Actually

now that I've thought on it a bit more, there is a part 3.

Style. Sometimes it just seems to fit the character and the script better to write out the more formal usage of a characters name.

In one of my scripts I have a character who is a big land baron.
He's stiff, formal and mean. I introduce him as Mr. MALCOLM and I keep him MR. MALCOLM in the dialog name.
It's a constant reminder who this guy is & his character in relation to everyone else.

When I'm dealing with a more affable character it seems to feel more natural to use only the first name.

Captain on deck

My vote, if it adds clarity then do it, and that includes his/her rank,

CAPTAIN JOHN "STUMPY" MICHAEL
Good morning!

FIRST OFFICER PERKINS
Morning, Captain.

ELIZABETH
Good morning John.

BARNACLE BILL
Avast there, Stumpy me old mate!

IRS OFFICIAL
Am I addressing Captain John "Stumpy" Michael?

CAPTAIN JOHN "STUMPY" MICHAEL
Er, yes...?

Let the Force guide your typing finger.

-Derek
Derek's Web Page - stories, screenplays, novels, insanity.

character names in dialogue

Batman Begins - 4 names:
Young Bruce
Bruce
Wayne
Batman
- all the same character (only young bruce was played by a different actor) and i'm sure the reader understood

don't sweat the small stuff. just do what works!

Spoiler - Batman's identity revealed!

Nikee, that's kinda different -- is there any moviegoer on the planet who doesn't know Bruce Wayne is Batman? So the writers don't need to worry about different character name(s) causing confusion, everyone reading the script already knows who Young Bruce and Bruce and Wayne and Batman are (or is).

I've got a character in one of my scripts called Lieutenant Jane Lacey. When she's addressed formally she's "Lieutenant" but when her friends address her they use her nickname, "Lace" so in the script calling her LACEY to tie in with her spoken nickname made more sense than calling her JANE (since no one ever calls her Jane except her father, and he's in a coma). Usually I call female characters by their first name and male characters by their surname, which is a helpful reminder of their sex if nothing else, but on this occasion the most often-used (phonetically) name won.

If any of that makes sense, it's a miracle.

-Derek
Derek's Web Page - stories, screenplays, novels, insanity.