There isn't any one trick to finding them. If you see a distant wisplight, you should always go check it out, and if you hear seekers around you, it's a good idea to search the surroundings in case there's dungeon entrance.

Whether sailing will be more helpful or just legging it is down to player preference and map generation. Both methods can help a lot in establishing how large the region is and how many dungeons there might be, they are pretty well spaced out, comparable of frost caves IMO.