I just got back from Whitehorse where I taught a workshop on pitching to some very hard-working participants who had both TV series and feature projects under their arm.
I had a full two days planned and could probably have used another half day to get through everything. It's like when I was in school. I was an A student - not because I was smart, but because I decided I could ace tests if I just made sure that any question the teacher could ask I could answer. I think you need to take the same approach preparing to pitch.
As I said to the workshop students, you're pitching to someone who is looking for ANY reason to say no. Your job is not to give them a reason.
That means your concept has to be rock solid. It may not be what they want, but you don't want them to fault you on quality, just on taste. It's like you're building cars. There's no way you can sell your car to someone who's looking to buy a sink. But you must make your car a Mercedes, not a Yugo, so that when you get a chance to sell to someone who wants a car, they can't fault you on quality.
You also need to make sure your concept has a strong enough franchise, especially if it's a TV series, for them to "get" it and see what it can be week to week.
Know yourself, who the audience for your show will be. Not in demographic-speak but in terms of interest. "My show appeals to people who care about the environment and who like mysteries." I think that's a legitimate description of an audience, regardless of whether that's women 18-35.
Make sure the characters fulfill the audience's need for archetypes. It doesn't mean you have to slavishly provide the same old archetypes with your characters, but figure out what archetypal roles your characters provide.
Be sure you know whether your show has legs to provide enough story potential to create multiple episodes. Have at least half a dozen episode ideas going into your pitch session.
And work out whether your show has enough potential for at least a first season arc.
Having all of this in your arsenal means that they can't ask you something you don't know. Just like my high school teachers couldn't. It's a lot of work, but it's what it takes to buy a ticket to the lottery.