Study current TV shows and pay attention to their pilot episode. Most of the networks now post these online at their websites, or they may be available at your local library. Pick one or two and write a beat outline of the major scenes. This will give you an idea of what you have to include in your spec script.
Now write your script in standard TV format. Using a scriptwriting software program like Final Draft helps. If this is an hour long show then about 60 pages will be your script length.
Unlike other scripts for your series, if you sell it, the pilot script has to present the basic concept for the show, introduce the major characters and establish the locations, whether it's Los Angeles, Hawaii or Mars.
When you finish your first draft, reread it and do a polish as needed. Now you're ready to take it to market.
Get a copy of the HOLLYWOOD CREATIVE DIRECTORY - PRODUCERS EDITION. It lists all the production companies in L.A. and New York. It also lists the current TV shows, networks and studios, with the key personnel and their titles. These are the folks you want to read your script.
You'll also want to work up a SERIES BIBLE that covers the basics of your show. This includes concepts, characters, and the kind of stories you'll be telling.
At this point you'll need an agent. If you don't have one,say you have a lawyer. This can be any lawyer that you know or are related to. Or you can have a friend start a management company and be your manager. And, of course, this script can be a great tool for getting an agent.