Generally, its recommended to book flights about 6 months in advance to secure the best deals. However, prices can vary, so it’s a good idea to monitor fare trends and set up price alerts for your specific travel dates to catch any potential discounts.

Flights from Cincinnati can be pricey. If you're looking to save, consider flying out of a major hub like New York City (JFK or Newark EWR), Chicago (ORD), or Washington, D.C. (IAD). These cities often have more competitive fares and better flight options.

If you're planning to visit another destination after Lisbon, consider using the Google Flights multi-city option. This feature allows you to view flight options from multiple cities, potentially saving you from having to fly back to Lisbon. It's a fantastic way to explore more of Europe without doubling back, making your travel experience more efficient and enjoyable.