It depends. On or off the bike my philosophy for travel is generally to never pre-book anything unless flying internationally or going to some major city where walking around to find a hotel is too tedious/time consuming/expensive (on a "waste half a room-night" basis). This is less of a valid exception when cycle touring, since it is so easy to cover ground on a bike, but cycling around dense Asian cities is no fun like Europe. Usually, out of a city, it's always a combination of destination research and satellite view / Google Earth. I look for small roads, vague estimates of the topography, and major sites of interest en-route. Things frequently worth stopping for by bike that car people miss are numerous: bridges, views, caves, villages, botanic gardens, waterfalls, beaches, festivals, weddings, funerals, markets, landslides, bullfights, wild animals, botany, insects, roadside vendors, food, historic plaques, locals, kids, etc. To be really relaxed and up for anything you don't want to fix your timing, so forward planning is a no-no. Research is completed when you have a general idea of topography and a general idea of what to deviate, look or stop for en-route, and a couple of towns that might be viable for end-of-stage.