Subtle Grammatical Usage Notes

• By Contrast / In Contrast
  Use By contrast when the next word is a noun. Use In contrast when followed by a preposition such as "with" or "to". (REL)
• Complimentary / Complementary
  Complimentary means praising or free of charge. Two things are complementary when they combine in a way that enhances each other's qualities or if they are nucleic acid bases that pair with each other. Thus, "complementary base", "complementary skills", "complimentary comments".
• This Data / These Data
  Use this data when you can replace "data" with "information". Use these data when you can replace "data" with "facts". (source)

• Principle / Principal
  Principle means the fundamental basis of a fact. A Principal is the main player or the person of most importance in a project. Thus, "proof of principle", "principal investigator", "in principle", "the principle reason", "school principal".
• Regardless / Irregardless
  Regardless is correct. Irregardless is a commonly heard but incorrect term, probably originating due to similar word pairs like respective / irrespective.
• Where / Wherein
  Use wherein when you can replace with "in which" or "in what".

Punctuation

• Generally the best way to use Greek letters, etc., is to use the "Insert symbol" command in a program (like Word or Illustrator), rather than symbol font. This generally causes fewer problems across programs or platforms.
• Hyphen, en dash, em dash

Avoid