The word "día" is masculine.

Although the word "día" ends with the letter a, it is a masculine noun. As such, it requires the use of masculine articles and adjectives - el día (not la día) - buenos días (not buenas días) -- el otro día (not la otra día).

Do not translate word for word.

Direct, word-for-word translation often leads to mistakes. One example is the sentence, "I'm going to buy a pair of pants." When this is translated to Spanish, the words "a pair of" are dropped. A correct translation would be, "Voy a comprar pantalones."

Use "ser" to tell where an event is taking place.

Early in your studies, you probably learned that "estar" is always used to denote location. When it comes to events, this can be confusing. "Ser" is always used to tell where an event is taking place. "El perro está en la casa," but "La fiesta es en la casa."

The words "aquí" and "acá" are not interchangeable.

"Aquí" and "acá" both refer to a location that is close to the speaker. These words are not interchangeable. "Acá" is used with verbs of motion, while "aquí" is used in other instances. "Juan, ven acá." (John, come here.) Puedes registrarte aquí. (You can register here.)

Misuse of the term "American."

In the United States, it is common for one to refer to himself as an "American". However, Spanish speaking people consider anyone from either North America or South America to be an "americano". If you are from the United States, use the phrase "Soy de los Estados Unidos" (I am from the United States) to avoid confusion and to avoid offending people. 

Don't confuse "date" with "date."

To express "date" as in "What is the date?" -- use the word "fecha." To express "date" as in "an appointment with someone" -- use the word "cita".

Don't overuse "yo."

Because English requires a noun or pronoun be used for the subject of the sentence, it is common for the beginning student to think that the same is true in Spanish. In Spanish, the subject of the sentence is frequently conveyed by the ending of the verb: "quiero" means "I want" -- there is no need to include the subject "yo". In fact, if you were to constantly use "yo" in your speech, you would come across sounding quite self-centered. Avoid using the word "yo" as the subject of a sentence, except for emphasis: "Ella quiere ir al cine pero yo no quiero." (She wants to go to the movies but I don't.) Here it is acceptable to use "yo" because you are emphasizing the difference between what you want and what she wants. Remember, unless you want to call attention to yourself, leave out the word "yo".

hopefully that helps you guys :)