Study the alphabet. The Greek alphabet comprises 24 letters, most of which produce sounds similar to their Latin alphabet counterparts. For example, O (omicron) is used more or less the same, but the letter B (vita) produces the sound of the letter V in English.
Stress words on the vowel with the accent mark above it. It's like an apostrophe, placed on top of vowels. Once you learn the sounds of each letter, reading text will become easy, even if you can't yet understand the meaning.
Form sentences using the subject+verb+object construction for active voice and the opposite for passive. Passive voice is not formed using auxiliary verbs; every category of verbs (verbs teamed according to their last syllable or the stress) has its own passive voice, so you must study each of them separately.
Use punctuation marks the same way you would in English, with a few exceptions. For instance, the semicolon is the Greek question mark. Where you would use a semicolon in English, Greek uses a mark called "ano telia," an upper period.
Practice the different genders of adjectives. Every noun can be either masculine, feminine or neuter, and adjectives -- as well as articles -- must follow suit. For example, in English you say "the good father" and "the good mother," but in Greek, the word for "good" changes from "kalos" to "kali," depending on whether the noun it's referring to is masculine or feminine.
Read children's books in Greek, or practice your basic Greek knowledge through BBC's Greek language lessons (see Resources). Your biggest challenges at this point will likely be learning the vocabulary and advanced grammar rules.