Well, I finally decided to write about a book that isn't completely useless when it comes to writing spec scripts. In fact, I would go as far as to say that 'Elephant Bucks' - by Sheldon Bull - is the best how-to sitcom book out there.
There are numerous reasons why the book is better than the rest out there and one of the most important reasons is that the book actually makes sense. By that I mean that after you read it, the chances are that you might start writing and stop procrastinating. At least that's what happened to me.
So, the book has a great section about structure. It gives you seven plot elements that you should think about when you're trying to come up with a story/storyline. (depending on your character, active or passive, these are first goal/problem, obstacle, first action, act break, second problem/goal, second action and resolution).
The reason that this section is so good and helpful is that it concentrates on characters and what motivates them. Nothing is more important than your characters wanting or needing to solve something. If your characters don't have a goal or a problem, they're stuck in a room doing nothing like Penny, Amy & Bernadette on the Big Bang Theory.
Perhaps the most important thing that I learned about structure is the 'first action', which Sheldon calls 'an unwise decision'. This decision is important, because when your character does something, ahem, unwise, that action can develope into an actual storyline - not just into a series of pointless 'and then' scenes that South Park's Trey Parker has talked about.
It is of course up to you to come up with those ideas, but 'unwise decision' is a much easier term to understand than the usual 'inciting incident'. I still haven't figured out what that really means. I don't think there's any reason to make structure intentionally difficult to understand and Sheldon, unlike others, makes it pretty easy for the reader (he really does).
The way Sheldon's book differs from all those others, is that in 'Elephant Bucks', he actually writes an episode with us (Frasier). This is such a simple idea and it works beautifully because we get to read how Sheldon plans his episode and what his thought processes throughout the script are. He goes step by step through those seven plot elements, and voila, in the end it turns out we have come up with pretty good storylines and a script.
Other than that, there's stuff like editing your script and how to rewrite dialogue among other things that are really valuable. Brevity in scriptwriting is usually a virtue, so it doesn't hurt that Sheldon chimes in on that.
I also have to say that there's another big gem in the book besides that 'unwise decision' and that is Sheldon's advice that you should write your script as a drama first. After all, jokes are easy, storytelling isn't.
That's my advice to you too, because if you find a way to tell a dramatic story without threatening the status quo (character relations), you're almost bound to write better scripts than even the showrunners on their shows. If you understand drama and characters, you really don't need to understand much else.
Besides teaching us how to write a script, the book also has a second part which is about landing your job as writer. There's a lot of stuff about being a writer on a show, about agents, how to deal with network executives, what it feels like when you get rewritten and other useful things about how you should prepare yourself when you get your lucky break.
All in all, Elephant Bucks is one the very few books out there that actually makes sense and doesn't confuse you. What more as a writer can you ask for?