The English spoken at the time of King James is far different from the English spoken in this day and age. In fact, the language of the King James Bible is much closer to that of Shakespeare. Reading other works in the English of the period will give you practice for when you sit down with the King James Bible. Keep a good dictionary handy for words that have fallen out of general use.
The King James Version of the Bible is not, of course, the language that the Bible originally was written in. The Bible comes from a variety of Classical Hebrew, Aramaic and Greek sources. Concordances are Bible study aids that help you understand the meaning behind the meaning. These texts, indispensable for serious Bible study, tell you everywhere that a word appears in the Bible. Thorough concordances, such as Strong's, also include a Hebrew and Greek dictionary at the back so you can find out the meanings of words used in the original source material.
Particularly because the King James Version of the Bible is written in archaic language, it is important to take close and careful notes. This helps you to remember specific key points, as well as knowing where to look when one part of the Bible explicitly references another or just seems to.
Having another version of the Bible handy helps you to understand what you are reading. While your primary focus of study is the King James Version, "paraphrase" versions of the Bible that do not attempt to translate the original source materials, but merely paraphrase the KJV in more modern language, are helpful in getting the gist of the passage. You can then refer to the KJV to get the finer nuances of the text.
Whether you are a committed fundamentalist Christian or a secular student reading the Bible as literature, there are a number of study guides out there for the King James Bible. You can even get versions of the King James Bible that have a number of annotations, allowing you to get the extra information you need without ever cracking another book.