US: fill out (a form)

UK: fill in (a form)

Further / Farther

Further - refers to an extension of time or degree; e.g., “We need to study this further.”

Farther - refers to length or distance; e.g., “I went farther north.”

Envelop - verb

Envelope - noun

Dwarfs / Dwarves

“Dwarfs” is correct.

“Dwarves” used by Tolkien, and widely adopted ever after

Pesky North, South, East, West

Points of compass: small first letters - north, south, east, west.

Regions: Capitalized first letters - I’ll be in the North; I’m heading South; I’m a Northerner.

Descriptions of places: small first letters - eastern Siberia; western France.

Descriptions of widely-known places: capitalized first letters - Southern California; Lower East Side.

Dad, Mum - capitalized first letters only when used as a substitute for the name as a term of address (“hey, Dad!”); all other times - dad, mum.  (AP Style)

“Best-seller” not “bestseller”, according to AP (US English).  (Hyphen-Hell).

“Have/Has Been” - Not “Is”

If something has been happening - and is still happening - “have/has been” is used. In some foreign languages, the present tense is used - “the agreement is in force ten years” - but this would have to be “the agreement has been in force ten years” in English.

“Fact” Avoidance

Use of “fact”, as in “proving the fact that…” not used in English like in some other languages (when a “fact” has yet to be established/confirmed)

Examples:

“To prove the fact that he left the country” - possible; but, better: “To prove whether/if he left the country”

“Documents that confirmed the fact of the export” - better: “Documents that confirmed that the goods were exported”

But on its own - “We need to prove the fact” - possible!

% / Percentage Points

Percentage points are the unit for the arithmetic difference of two percentages

That is, rises or falls in pecentages are measured in percentage points, not percent

E.g.: Home computer possession in 1990 stood at 5%; in 2010 it was 70%. So, there was an increase of 65 percentage points, not 65% (the increase was ~93% if the population remained constant)

No./Nos.

E.g., “Addendums (or Addenda) Nos. 1, 2 and 3”;
not “Addendum(s) No. 1, 2 and 3”;
never “Addendum(s) NN 1, 2 and 3”;
never “Addendum(s) N. 1, 2 and 3”.

“Ms.” (US) / “Ms” (UK), not “Miss” or “Mrs(.)”

Miss & Mrs./Mrs considered non-PC.

Separate Words

“Mr. Smith” (US) or “Mr Smith” (UK) (i.e., with a space); not “Mr.Smith” or “MrSmith” (without). Similarly, “St. Petersburg”, not “St.Petersburg”, etc.

US: Mr.

UK: Mr

To “serve notice” - *very* formal giving (serving) of notice of, e.g., writs

To “give notice” is used in most/all cases when a court is not somehow connected, e.g., giving notice to a landlord/counterparty/friend of some intention; to serve notice in such cases would, to most people, not be correct English, although some would say it’s ok (http://idioms.thefreedictionary.com/serve+notice)