There is a lot of confusion about the use of abbreviations and acronyms. Consult the AP Stylebook under "abbreviations and acronyms." Often there'll be an individual alphabetical listing for the abbreviation or acronym in question.
Confusion about abbreviations and acronyms stems from the fact that there are so many exceptions.
Here are some grammar/style/punctuation issues that come up frequently at the College of engineering:
1.1 Do not abbreviate "university" or "department."

• Right: The students from each department visited each university in the state.
• Wrong: The students from each dept. visited each univ. in the state.

1.2 Use "U-M" to abbreviate "University of Michigan." (Always spell out the first use.)

1.3. Do not use periods with abbreviations for units of measure. (AP exception)

• Right: The speed limit is 35mph. The rock was 20mm wide.
• Wrong: The speed limit is 35m.p.h. The rock was 20m.m. wide.

1.4. Do not put a space between a number and a unit of measure. (AP exception)

• Right: The speed limit is 35mph. The rock was 20mm wide.
• Wrong: The speed limit is 35 m.p.h. The rock was 20 m.m. wide.

1.5. Do not abbreviate titles in text. It is acceptable to abbreviate titles when space is an issue. (e.g., in tables, columns, graphics, etc.)

• Right: The student consulted with Professor Smith.
• Wrong: The student consulted with Prof. Smith.

1.6. Abbreviate United States when it's an adjective. Use the full name when it's a noun.

• The U.S. policy applies to the College.
• The College of Engineering ranks among the finest engineering colleges in the United States.

1.7. Do not punctuate acronyms.

• BSE, ME, PhD
  (See "Acronyms Commonly Used in the College of Engineering" at the end of this Guide for a complete listing of acronyms in general use at U-M.)

1.8. MEMS

• The correct spelling for the expansion of MEMS is "microelectromechanical systems" - no interior caps, no hyphens.