1. Look up words carefully. Use the clues the English-German part of your dictionary gives you as to which German expression is most appropriate for what you want to check; then check the word or expression you come up with in the German-English part of your dictionary to make sure it really does what you want. This is a lot of work, and so before you look up a word, you should consider whether you might not be able to express the same idea more simply in another way using the vocabulary you already know!
2. I am 17/18 = Ich bin 17/18 ODER Ich bin 17/18 Jahre alt.
3. Remember "gern" is for verbs and "mögen" is for nouns: Ich schwimme gern; Ich mag SPAM.
4. German has no real equivalent to the verb "graduate." The verb "graduieren" exists, but is very awkward. Try to say things like "Nach [=after] der High School…" or "Wenn ich mit der Universität fertig [=finished] bin…" or "Ich mache meinen Abschluß…" [="I complete my degree"].
5. Be sure to look up the plural forms of nouns if you don't know them!
6. UofM is "Die University of Michigan" or "Die Universität Michigan"; "High School" is "High School" ["Hochschule" actually refers to colleges/universities in German].
7. Avoid beginning sentences with "auch." Put "auch" before the thing shared in common.
8. German adjectives come before the noun, like in English [for those of you who have had Spanish, Italian, or French].
9. Freshman = Freshman ODER Student im ersten/zweiten Semester. Or you can say "Es ist mein erstes Jahr an der Uni." Sophomore ==> drittes/viertes Semester; Junior ==> fünftes/sechstes Semester etc.
10. At 5 o'clock = Um 5 Uhr, but to say you are at a place, you need to use "in" or occasionally "an," never "um."
11. "Ich" is not capitalized in German except at the beginning of a sentence. But all nouns are capitalized.
12. "Die Familie" and "die Polizei" are singular; "die Leute" are plural.
13. ie/ei (spelling)
14. VERB SECOND!!