Default to first mention in Collins/Webster’s in most cases (capitalisation is an exception), for example amid, not amidst and among, not amongst. Refer to relevant style sheets for specific regional spelling lists.
For text following British spelling, when Collins gives a choice between -ise or -ize use the -ise version. Collins/Merriam takes precedence when dealing with compound words, not CMoS.
The following standard Lonely Planet spellings deviate from Collins and/or Webster’s.
air-conditioning
alfresco
cafe
checklist
ebook
ecofriendly
guesthouse
homemade
internet
midrange
offline
organisation [US: organization]
phrasebook
postwar
rainforest
secondhand
uber (eg ubercool; close up unless hyphen needed for clarity)
web (as in the www)
webpage
wi-fi