Honorifics (These are especially important!!)

In Japanese, the last part of the name is usually the equivalent of the first name, so a name like Watari Sakura, Sakura is the First name, and Watari is the Family name, or surname.

That being said, Honorifics are used in every day speach, pay special attention, because in most cases, lack of an honorific is considered to be insulting.

-San: is the most common honorific and is a title of respect. It is used for the surnames or given names of both males and females. Although in translation san is usually rendered as a common courtesy title like "Mr." or "Ms.", unlike these it is never used in self-reference. Using san to refer to oneself makes one appear childish or incredibly vain.

-Kun: s an informal honorific primarily used towards males (it is still used towards females, but rarely). It is used by persons of senior status in addressing those of junior status, by males of roughly the same age and status when addressing each other, and by anyone in addressing male children. It can also be used by females when addressing a male that they are emotionally attached to. Usually it depends on the relationship between the two people. In business settings, women, particularly young women, may also be addressed as kun by older males of senior status. It is sometimes used towards male pets as well.

TEACHER CHARACTERS!! School teachers typically address male students using kun, while female students are addressed as san or chan. The use of kun to address male children is similar to the use of san when addressing adults. In other words, not using kun would be considered rude in most situations, but, like the rule for using san in reference to family members, kun is traditionally not used when addressing or referring to one's own child (unless kun is part of a nickname: "Akira-kun"—Akkun).

-Chan: is a diminutive suffix. It is an informal version of san used to address children and female family members. It may also be used towards animals, lovers, intimate friends, and people whom one has known since childhood. Chan continues to be used as a term of endearment, especially for girls, into adulthood. Parents often call their daughters chan and their sons kun throughout their lives, though chan can be used towards boys just as easily, in particular if it results in a nickname that is particularly pleasing to the ear; such nicknames often spread outside the family circle during the school years. This is still considered very feminine. Adults may use chan as a term of endearment to women with whom they are on close terms.

"Pet names" are often made by attaching chan to a truncated stem of a name. This implies even greater intimacy than simply attaching it to the full name. So for example, a pet rabbit (usagi) might be called usa-chan rather than usagi-chan

-Sempai: is used to address senior colleagues or mentor figures, e.g. students referring to or addressing more senior students in schools, junior athletes more senior ones in a sports club, or a mentor or more experienced or senior colleague in a business environment. As with English titles such as Doctor, senpai can be used either by itself as a title, or with a person's name in place of san.

-Kohai: is the reverse of this. It is used to refer to juniors, but not normally to address them: kōhai are normally addressed by name +kun (addressing someone directly as kōhai would be somewhat rude).

-Sensei: is used to refer to or address teachers, practitioners of a profession such as doctors and lawyers, politicians, and other authority figures. It is used to show respect to someone who has achieved a certain level of mastery in an art form or some other skill. Sensei can also be used fawningly, as evinced by adherents in addressing or talking about charismatic business, political, and religious leaders (especially unordained ones).

-Sama: is the formal version of san. This honorific is used primarily in addressing persons much higher in rank than oneself and in commercial and business settings to address and refer to customers.

-Dono: One of the most formal of Honorifics, it means Lord, or Master.

Lack of honorific: The most important. While it is often considered insulting, there is only a few cases where it isn't. This is usually reserved for the most intimate of friends and lovers, or with family, although, with family, the name is more often substituted with a pet-name or with one of the following Family nouns.

Special thanks to Wikipedia for providing me with a quick copy paste, as opposed to typing this all out myself. >_<

Family Nouns!
Okaasan - Mother
Otousan - Father
Oniisan - Brother (Also Niisan). Oniisan can is also used by younger girls to refer to older men that they look up to. Can also be used by younger female lover to an older Male lover in a younger couple, where there is a substantial gap between the two.
Oneechan - Sister(Also Neechan). Is also used by younger children to refer to an older girl they look up to, more common in girls than boys.

Other Words and Phrases
Arigato - Thank you.
Doozo - Please
Hai - Yes
Iie - No - This is considered in some cases to be impolite, because it is a direct negative, when not wanting to sound impolite Chotto is often used. Direct translation of Chotto means Not Really.
Kawaii - Cute
Yoshu - Good

Less common words that might come up
Ofuda - Anti-Evil Scrolls used by Shinto Priests.
Oni - Demon
Yoma - Ghost