Recommended reading - The Making of Star Trek, by Stephen E. Whitfield & Gene Roddenberry (1986):

The Making of Star Trek

By Stephen E. Whitfield & Gene Roddenberry.

Published by Del Rey.
Twenty Second Printing edition.
Published 1986.
Mass Market Paperback.
ISBN-10: 0345340191
ISBN-13: 978-0345340191

Description:

"For would-be TV writers, directors and producers, this will be an education in itself, a polished but non-varnished look at how TV really works." – Publishers Weekly.

A complete history of what may be the most popular TV series ever – the original Star Trek episodes! Filled with quotations from cast members, memos to and from Gene Roddenberry, biographies of cast members, sketches, photographs, set descriptions, and even budgets and cast schedules, this volume is a fascinating, invaluable behind-the-scenes account of the development and production of the original Star Trek series.