Build around itineraries, not around countries. "Two weeks in Vietnam and Cambodia with two internal flights" is a search with a person behind it who has already spent an evening failing to assemble it; "holidays to Asia" is a search you will never outrank.
Write for the moment the plan gets complicated. Somebody trying to fly four people from two different cities to one wedding, or to route a trip around a passport that expires in November, has stopped comparing prices and started looking for help.
Treat protection as content rather than as small print. What ATOL covers, what it doesn't, and what happens if an airline stops flying are things people search for after reading a news story — and the agency that explains it gets remembered when they book.
Keep the destination pages honest about season. Half the value an agent adds is saying that a place is unbearable in August or shut in February, and pages that say so read as advice instead of as advertising.