Aside from the obvious difference of a movie script been one complete story and a tv series been a continuing story across several episodes. Is anyone aware of anything you would do differently before or during writing a tv series script
TV series, if they take outside scripts (some are only written internally), will sometimes have "protected characters" and "protected topics", that may not even be the main character, but your story cannot focus on that character.
For example, Star Trek: The Next Generation took many outside scripts, but Wesley Crusher was a protected character, and although Data (the artificial life form) was not, Data's emotions were a protected topic. So you could write a story that centered on Data or made Data the hero of the episode, but your script cannot "change" Data or his struggle with emotions, you can't give him a clue or have him make a discovery that will lead to that. The topic of "evolving" Data was off-limits.
A similar thing applies to other series; you can usually guess just by watching the series which are the protected characters and topics: The stories that would be the most interesting to write, to advance some character emotionally or some relationship between characters, or to solve some problem (technical or academic) a character has struggled with.
There are many exceptions, but in general the trick of a series that is NOT like a movie is that the repeating characters in the series (often both heroes and villains) have very, very flat character arcs. They finish the episode as exactly the same people they were when they started the episode. You can say, "Oh, but they learned a valuable lesson," but whatever the lesson is, it cannot change anything about any future episode. It cannot make the character a different person emotionally, or in skill or humor or anything else. Nobody becomes a killer or criminal for the first time, nobody finds out they fathered a child without knowing it. No new characters are introduced that plausibility would demand must be in future episodes: If it is plausible for one of the main characters to have a fling with a new romantic partner, the new guy/gal should probably be dead or otherwise forever gone by the end of the episode (as might happen in a series focused on a group of single friends, e.g. The Big Bang, That Seventies Show, ST:TNG, etc).
The outside script uses the main characters as they are (personality, emotionally, physically), and leaves them as they are, as if nothing ever happened.
This is because the writers of a series write with the intent of making a franchise and keeping the characters forever, perhaps over a hundred episodes. As if the series could go on for ten years or more. Repeating characters do change, but those changes are planned and up to the staff writers over many episodes, often to sustain suspense over many episodes: So yes, at the end of Season 2 Jack finally kisses Jill, and we wait six months to see what happens next. Eventually Jack and Jill date, have sex, get married, have children, whatever: Those are major character changes to be sure, but the domain of staff writers, used judiciously and slowly to sustain interest in their series. Most modern series (unlike, say, MASH), have intentional long, multi-season back stories. It is tempting to write an episode that takes a step in one or more arcs, just because you yourself (as a writer) feel the tension and want it resolved. But keep in mind even if you sell a script, it may not see air for a year, and you have no sure idea where the long plot is going to be by then.
You can often guess if a series takes outside scripts by looking through the writing credits of episodes. If it is always the same small group of names, maybe not. If you see some one-off authors that don't repeat, they probably do. I haven't looked into this for more than a decade, but good candidates might be series like "Elementary". Come up with a clever mystery, Sherlock and Watson unravel it, and nothing else about them has to change. To me that is the perfect prototype of a series I would target: Anything where the character(s) frequently find themselves in a new setting, dealing with new people we never saw before and will never see again, typically resolve the challenge and return to home base.
Other series about "teams" could be similar, "Blindspot" episodes were centered around mysteries too (the tattoos), some of which were one-off episodes. The "X-Files" reboot perhaps. Or some of the combat team shows, or detective series, or cop series.
Series like "Vikings" do not look ripe to me, every episode is making small but significant advances in the saga and the audience expects that. I'd leave alone any series in which main character relationships are evolving and changing fairly rapidly, and you (as a writer) don't even know if the characters you want to write about will be alive or still in the mix next season.
Keep in mind that over the transom scripts are accepted because they are relatively cheap and take a week's worth of pressure off the staff writers (well not quite a week, they still have to review and rewrite whatever you turn in, for voice and perhaps to interject a minute or two of whatever main character development they might want, or to repair things they know about characters or future relationships that you did not).
So I'm not sure if this next thing I say is good advice or not, but I would write MY episode tight but a page (for an hour) or half page (for a half hour) short. One page = one minute of screen time, currently major networks average 21 minutes of screen time for a half hour show, and 43 minutes for a one hour show, but this may vary and you should stopwatch a few episodes of your target to be sure of what their time budget is. It doesn't hurt to stopwatch where their commercial breaks occur, your script will be more acceptable if scenes break where they should and suspense is sustained over the commercial break, and if they have an opening setup of a minute or two before the title sequence, you should be writing one too (e.g. the crime being committed or discovered in a detective series, or ST:TNG always had a teaser set up).
This gives staff writers room to extend some dialogue or even add a few shots or a scene to interject any elements of a multi-episode back-story they might want, and it is always a hundred times easier to lengthen a tight script and keep it cohesive and rational, than it is to cut a tight script without losing anything important.