Choose a spelling system, American spelling or British spelling or any other variety.
If you want to use British spelling: Consider using -ize instead of -ise (Oxford spelling). Both are correct in British English. The suffix -ize is more international, where -ise is more British. Consider dropping the letter 'e' is some words: judgment instead of judgement, aging instead of ageing.
If you want to use American spelling: Consider using double l's in words like traveller, labelled, cancelled. Consider using theatre, glamour and grey instead of theater, glamor and gray.