Common word abbreviations include "ASAP," "P.S.," "RSVP," "BYOB" and "etc." Titles, such as mister and doctor, are often abbreviated, as well as degrees, such as bachelor of the arts.
ASAP means "as soon as possible." P.S. stands for "post script," and it's typically used after a message to add an extra thought. It's most common in formats that don't allow the writer to edit his message, such as typewritten or handwritten letters.
RSVP comes from a French phrase, "Répondez s'il vous plait," which translates to "Respond, if you please." People often use this abbreviation for event invitations to determine the number of guests attending, as it asks guests to respond with an indication of whether or not they're going.
BYOB stands for "bring your own bottle," although some interpretations substitute "beverage," "booze" or "beer" for bottle. Event invitations include this abbreviation if the host isn't providing beverages. Certain businesses, such as bars and restaurants, include this abbreviation and allow guests to bring their own beverages.
Etc. stands for "et cetera." It originates from a Latin phrase that means "and the rest (of such things)." A typical usages of the abbreviation is in writing to indicate a logical continuation of a series.
Mr. is the abbreviation for mister, which is a title for a man. Dr. is the abbreviation for doctor. Degree abbreviations typically use the first letter of the degree and field, such as the abbreviation "B.A." for bachelor of the arts.