Develop a solid main character for the series with well defined traits. Then create a clear compelling outline of this character and make it the starting point of your pitch. The executives you are presenting to will need to understand the motivations of the main character. Consider the character of Homer Simpson, the lovable loser who, though far from perfect, generally does the right thing in the end. Then there the character of Batman, a dark loner driven by inner demons to protect the innocent.
Discuss the overall world your series is set in. Here you will want to create a background for the main character to act in, as well as the other characters, who you can now introduce as well. In the case of Homer Simpson, this world is Springfield, which is populated by a huge cast of wacky characters for Homer to interact with. Batman's world is Gotham, a gothic crime ridden city where Batman hunts the criminals.
Include artwork for your presentation, but only if you are able to create truly professional level work. While good artwork can help to sell an idea, bad artwork can kill the deal, even if the idea is otherwise a good one.
Decide on the role that you want to play with the show---such as producer, writer or artist---if it is picked up. If the executives you are speaking to ask about this, you want to be able to give a clear answer. You don't want to imply that you plan to wear many different hats, since this will tell the executives they are dealing with an amateur.
Prepare scripts for two completed episodes, so that the executives can see the characters in action. Create outlines for several more stories so that the executives have some idea of the overall direction of the series.