Research the TCPA, the Telephone Consumer Protection Act, since this is the law that governs telemarketing in the United States. There are very specific laws and regulations when dealing with a telemarketing script, and they must be followed. The penalties are stiff if you do not comply.
Write the script on a computer, if at all possible. This allows you to make an infinite number of changes, and gives you the opportunity to experiment with different pitches.
Use strong action words. Words such as "I will" and "You should." These will get the customer's attention, and keep it. By gripping the prospective customer at the outset of the call, you stand a better chance of getting a positive response.
Use the customers last name within the few seconds of the start of your call. Insert a place where the customer's name can be used comfortably at least once every 15 seconds. As children, humans are conditioned to respond positively to their names, and this will give you a much better chance of keeping them focused on you, instead of the room they're standing in.
Disclose three very specific pieces of information within the first 30 seconds of your call: Your real name, the company for which you are calling and the purpose of the call. For example, if you're selling insurance, you must disclose this within the first 30 seconds.
End your call with a "TCPA Close." This is a closing, which must contain the contact number and name of the company on whose behalf the call is being made. For example, "Thank you for your time, if you have any questions, please call <company's name> at <company's phone number>.
Write the script out. After you have a script written on your computer, you should write it out using pencil and paper. The act of writing the script on paper will help cement it in your mind, allowing you to move about the script comfortably, and pick up where you left off if you're interrupted.