First, clear enough icing on the bottom board before you drop an ingredient on the conveyor belt. If they are under, you will need lots of luck to bring them back. As the conveyor belt is 20-turns long, it is theorically possible to have an ingredient make a whole turn, but you should avoid that.
When an ingredient is dropped, or when there are 25 moves left, a new ingredient falls, so be very careful about the moves you do on the top board. Also, watch the conveyor belts and the vertical striped candies!