Learn how to pronounce words in German. In your textbook and dictionary, there should be guides to the consonant and vowel sounds that are different from English. For example, W is pronounced like English V, V is pronounced like English F, and J is pronounced like Y. Initial consonants may be sounded differently, like S at the beginning of a word sounding like Z, and ST and SP at the beginning of a word sounding like SHT and SHP. You will find two new characters: ess-tzet (ß), which stands for SZ, is transcribed as SS, and looks a little like a capital B; and the umlaut, which may appear over A, O, or U (Ă, Ŏ, and Ŭ). The two most difficult sounds for English speakers are the initial R, called an uvular R, because it's a little like clearing your throat, and the initial Z, which has more of a TS sound like the Z's in PIZZA.
Study the various forms of the pronouns and articles. It may be useful to put them all on one sheet of paper, because you will probably need to refer to it frequently at first. For example, where English just has the word THE, German inflects it differently depending on the case (whether it's the subject, direct object, indirect object, or possessive), the number (single or plural), and the gender (masculine, feminine, or neuter).
Memorize the number system. Once you learn the numbers one through 20, the rest are fairly easy. Be sure to learn both the cardinal and ordinal forms, like one/first (ein/erste) and two/second (zwei/zweite). Note that the ordinal forms take inflected endings similar to the articles. Because the numbers two and three are so close in sound (ZWEI and DREI), sometimes speakers will pronounce ZWEI as ZWO.
Build your vocabulary of German nouns. Try to learn them all with their definite article (der, die, or das), so that you get to know their gender. In some cases, gender follows rules, like following the gender of the subject (e.g., der Mann, die Frau), or making all nouns ending in diminutives (-chen or -lein) neuter (e.g., das Mădchen, das Entlein). You may see patterns depending on whether the noun ends in E or R as well. You may want to learn the plural forms as well now, because they have relatively few exceptions and are therefore fairly easy.
Learn the verbs, adjectives, prepositions, and adverbs next. Verbs take different endings and sometimes vowel shifts depending on the number and gender of their subject, for example "I see" and "he sees" would be "ich sehe" and "er sieht." Adjectives take different endings depending on the gender and function in the sentence of the noun they modify, and the endings are similar to the article endings. Prepositions determine the case of their subject; for example, the preposition UM (AROUND or ABOUT) always takes the dative case, and IN takes either accusative or dative case, depending on whether it indicates placement or direction. Adverbs function very similarly to English adverbs, but the preferred order if there are several in a sentence is different; in English we order them manner-place-time ("I quickly go home now."), and in German they are ordered time-manner-place ("Ich gehe jetzt schell zu Hause.").
Start learning the tenses, voices, and modes. Most past and perfect tense verbs in German follow a predictable pattern as in English; for example, "I hear, I heard, I have heard" becomes "Ich höre, ich hörte, ich habe gehört", and "I complain, I complained, I have complained" becomes "Ich klage, ich klagte, ich habe geklagt." English and German have similar roots, so the concept of irregular verbs will be familiar to you. You will often see similarities in the different tenses, as in "I drink, I drank, I have drunk" ("Ich trinke, ich trank, ich habe getrunken"). You will not need to use passive voice very often, but you should review it just so you understand it when you encounter it. Modes like the subjunctive mode will become more important when you get into translation later, but again, scan the rules so you become familiar with them.
Start putting your vocabulary words on index cards with the German word or phrase on one side, and the English on the other. You may want to include phrases that are common, like "zum Beispiel" ("for example"), and have multiple meanings when used in different contexts, such as "das Haus" ("the house"), "nach Hause" ("to the house/to home"), and "zu Hause" ("at the house/at home"). Test yourself by drawing the cards at random and seeing how quickly you come up with the correct answer.
Practice speaking and transcribing German. You can find recordings online of people speaking in German, and you may want to try instructional videos before interviews. Record your own voice reading a German text, and then come back to it periodically with a blank sheet of paper and try to transcribe what you had recorded.
Start doing written translations. Take a German news story or letter or speech, and use your dictionary to translate it into English. Do not cheat and use online translation programs, because you need to learn to do it for yourself and properly (online translators make lots of mistakes). Once you find yourself needing to look up fewer words in the dictionary, consider moving to more difficult translations like fiction and poetry. Keep in mind that when you try to read Germans writing casually as they do on message boards online, they may use slang and dialect words and phrases, and their spelling and grammar might be incorrect.