1. Spelling: This is the source of most differences. For American audiences, some common spelling differences include flavor vs. flavour; center vs. centre; traveling vs. travelling; recognize vs. recognise; etc. Setting the language/spellchecker in your word processor to "English (U.S)" will help catch most of these words.
2. Abbreviations & Acronyms: American English requires a period for abbreviated titles, such as Dr., Mr. and Gov. Most two-letter abbreviations are denoted by capital letters and periods, such as U.S., U.K. and B.A. For longer acronyms, caps are generally required (but not periods) for instances like FBI, CIA, BBC, DNA and NATO.
3. Idioms: There are several similar-looking idioms that have the same meanings but are expressed differently, such as touch wood vs. knock on wood; skeleton in the cupboard vs. skeleton in the closet; throw a spanner in the works vs. throw a wrench in the works, etc. Double-check your idioms to ensure you have the proper wording for American audiences.
4. Verbs & Prepositions: Note that some past and past participle forms can be regular or irregular. In British English, both forms are commonly used, but the irregular form (such as spilt, smelt and learnt) is rarely used in American English. The correct preposition may depend upon the context and situation. British English favors phrases like in a team and at the weekend, while American English favors on a team and on the weekend, respectively.
5. Ambiguous Words: There are words that are commonly used in both lexicons but have completely different meanings. For example, American football is not exactly the same as British football. Words like chips, torch, dummy and biscuit also carry different definitions.
6. Different Terminology: Some objects or phenomena are described by different words in British and American English. The most obvious examples include American fall vs. British autumn; trunk vs. boot; gas vs.petrol, elevator vs. lift; apartment vs. flat; sweater vs. jumper, etc.
7. Metric Vs. U.S. Customary System (Also Called Imperial Units): The metric system is used in the United Kingdom. However, American audiences are accustomed to the U.S. customary system, so please convert all measurements accordingly.
8. Cultural References: Be careful with the use of cultural references as they may not translate well — or at all — to American audiences. If you're not sure if they are applicable, don't use them.
9. Date & Time: Although many countries use the 24-hour clock and the little endian forms for dates (DD/MM/YYYY or DD/MM/YY ), you will need to convert it to a 12-hour notation (using a.m. and p.m.) and the middle endian forms (MM/DD/YYYY or MM/DD/YY ) for American readers.
10. AP Style: Please consult The Associated Press Stylebook for further editorial practices, as they differ from the BBC News Styleguide.