Candles and lanterns are place in different spots, because candles are placed on misty squares and lanterns are placed on clear squares, clearing adjacent misty ones. If you have a clear column then ignore it and place a candle on one of the spots in the next column.Does the 1st column (that happens to be free of blockages) need to be cleared, or is it kind of a clearing to get started. In other words, does the 1st candle need to be placed there, or in the next column where the gap lies between blockages?
I don't believe that it is efficient to try clearing every misty square. Don't be worried about the possibility of something lurking behind a square that you've missed. Be more concerned that if you go back and clear it you might potentially be unable to clear multiple squares later on. You should always think about the route that is clearing the most squares at a time, or that has the potential to open up the most squares.I think what can be confusing, is to de-mist all spots. Do you clear every single spot on the map, bar the obstacles, or just get an idea of what is where, and move on to try and find places that actually show hidden objects?
The grid is infinite, so there isn't ever a case of thinking there are a certain number of prizes in a certain area so I should try to find them. Just keep pressing on.