The invaluable Plain English Lexicon analyses 1200 words that occur frequently in British public-information documents. Which words will lay people understand? It's not as simple as choosing 1-syllable words over 3-syllable words every time.
The lexicon draws on research evidence in the US â€˜Living Word Vocabularyâ€™ and the British National Corpus of 100m words. Each word has a plainer alternative, and many have a recommendation for use. A few examples below will give you the flavour. As you'll see, the lexicon is realistic and practical, and entirely non-pedantic. It's kind to the poor public servant caught between a rock (bureaucratic jargon, some of which is useful) and a hard place (a too-rigid interpretation of plain English).
Martin Cutts of the UK Plain Language Commission prepared this valuable resource.