Skyscanner, google flights - I’ll usually have an ultimate destination in mind (e.g. Montevideo), and will then either find an acceptably cheap series of flights by turning off most of the filters, or setting up price alerts. Sometimes I’ll book months in advance, sometimes it’ll be “pack your bags, we’re going to Vladivostok... today!”

Also, my wife scours sites like https://www.holidaypirates.com/ which occasionally have some steals of deals.

Frankly the hardest bit has been organising catsitting.