Research the history and structure of Latin. Knowing some information about the grammatical rules and structures will help you in your studies. Theoretical knowledge will be especially helpful when only working with written materials, as you won't be able to learn and practice grammar in context as with spoken living languages. The website Latin Language includes information on many aspects of the Latin language and tips on learning it.
Study online. The website Omniglot features information on the Latin language as well as links to online Latin study courses and dictionaries. Once you have some of the basics of Latin grammar and vocabulary, you can start reading passages in Latin. Keep notes with new vocabulary and phrases that you learn so you can refer to them as you read. You can also teach yourself new vocabulary with flashcards. Though you will only be reading, it will be helpful to learn the pronunciation of new vocabulary so you can repeat new words to yourself. This will help you memorize them quickly. Look for an online course that will teach you the pronunciation of Latin.
Take a course in Latin. Many courses today are focused on reading only, as Latin is a dead language and is often taught with different objectives from living languages. Most university and community college courses teach Latin for the purpose of reading. Research the possibilities for registering for a single course at a nearby college. You may also be able to audit a Latin course, meaning you will be able to attend the course without officially enrolling and earning a grade. Even one semester can provide you with enough of a basis to continue study on your own and read the documents you are interested in learning in Latin.