Much has been written about the art of pitching. There are numerous books and programs from Save The Cat to Stephanie Palmer as well as pitch festivals that provide loads of opportunities to refine the art of the pitch. I suggest you investigate them all.
The key to a great pitch is simplicity. Find a way to introduce your pitch by telling a personal story. How did you get interested in the subject matter? Find a compelling or relatable way into your story. Use the hallway rule: make sure your pitch can be easily conveyed while walking someone down the hall. Have your pitch memorized, be ready to launch in at a moments notice as you never know who you’ll run into and when.
Keep the structure of your pitch simple: introduce the genre and arena, state the logline (no more than 2 or 3 sentences), describe the lead character(s) and then launch into the first 1/2 of the plot. If you’ve done a good pitch the responses are: “What happens next?” or “I’d like to read that.”
Always build from a simple idea. Be able to describe the basic plot of your story quickly. Keep your energy and enthusiasm up. If you don’t love telling your story it won’t be memorable or contagious.