Subject
While production companies want innovative and original ideas, a fresh treatment of a stock idea would also be welcomed. There is no need to strain your brain for something that has never ever been done before. After 50 years of sitcoms truly original ideas are a bit thin on the ground. There is a basic simplicity to most situation comedy that has to be recognised.
There are subjects that are said to be overdone which include the main two - student flat share and stately home - plus the office, the media and undertakers. Although an undertakers sitcom has recently been produced and I wouldn't be surprised if sitcoms from those other categories were being developed at the moment somewhere.
One network producer said recently that he doesn't want ensemble casts but star vehicles. A strong central character with fundamental personality problems but who isn't a complete bastard. Brittas Empire rather than Drop the Dead Donkey. But since then the network has commissioned an ensemble piece.
High concept or relationship based? One network producer told me he prefers high concept situation-led comedies like Red Dwarf; another network producer told me he prefers relationship based ones like Frasier. The trend at the moment is for the relationship based where the characters are with each other because they want to be. It has been said that the audience is losing faith in the scenario where you have very diverse characters trapped somewhere like a lighthouse, or a space shuttle or a lift. But maybe you can breath new life into that scenario.
William Goldman said in his book, Adventures in the Screen Trade, "nobody knows anything". Not the networks, not the prodcos and not me. Look at Cry Wolf. I don't think Alomo and the BBC said "let's produce an unfunny, unpopular sitcom." They genuinely thought it would work - until it was delivered at least. While there are certain guidelines it would be silly to ignore, I believe you stand more chance of success choosing a subject you care about, know about and believe has potential and longevity rather than second-guessing what producers or the audience want.
Longevity
There are times when I have danced about with joy having thought of a brilliant, original, clever sitcom idea only to discover that I couldn't think of any stories beyond the pilot. I never go forward with an idea unless I have at least one season's worth of stories, preferably two. If your setting and characters can't generate lots of potential stories then it will never be accepted.
Copyright
Copyright exists on any work from the moment it's written, and remains the property of the author unless it is 'assigned', i.e. formally given to a third party. However you can't copyright an idea.
You could, if you wanted to, take my God and Satan sharing a flat idea that I mentioned in Part 1 and prove me wrong by making it work. There is nothing I could do about it. Even if I had finished a God and Satan script you could still use the idea. You couldn't however use my characters, dialogue or scenes as that is clearly my creation.
This of course means that you could submit your sitcom to a producer and they could give the original premise to a more experienced writer to do something with. This happens so very rarely that it's not worth worrying about. In any case ideas are ten a penny, it's what you do with it that counts. As an aspiring professional writer, you should have lots of equally good or better ideas anyway.
There was one television comedy which was identical to one of my scripts. I thought about suing but as I had never shown my script to anyone there seemed little point. Certain ideas are going to occur to different writers at the same time, that's much more likely to happen than "idea theft". The BBC Talent 2000 competition had four scripts from different writers with the same title, setting and overall idea.
There are two sure ways of avoiding having your idea "stolen". 1) Don't send your script out until the execution is as good as your premise, that way there'll be no need to get someone else in. 2) Never send any scripts to anyone ever.
"Better to be occasionally cheated than perpetually suspicious." B.C. Forbes
Location/sets
Now you've got your characters and subject but where does it take place? Audience sitcoms are produced in a studio with room for three or four sets. A small amount of location filming may be possible; between three and five minutes. These factors limit the number of locations you can use in a script and may mean your initial subject matter isn't viable as a traditional studio sitcom. If that were the case, perhaps it would work as a single camera sitcom or comedy drama? Financial limitations may also prevent the use of exotic or difficult locations or complicated sets.
Part 1: Audience / Theme / Character
Part 2
Part 3: Story / Structure / Dialogue
Part 4: Duration / Format/ Submissions / Checklist
Part 5: BBC & C4 / Prodco / Next / Rejection / Acceptance / Agents