INSULATE THIS WAY
You want to place a layer that stops heat transfer in each direction for optimal energy conservation. Reflective foil sheeting underneath roof tiles (shiny side up), for instance, will reflect back radiation coming off of the hot tiles. Then there’s also a layer of glass-fibre insulation that you can put on the ceiling boards to further ward off heat transfer to the inside of the house.
If you have a house with exterior cavity walls, the air flowing through the cavity acts as a heat-transfer retardant. You can request insulation in cement-block houses during construction, but good luck with that. Best bet is to invest in good paint. Double-glazed windows have become requirements with the more energy-conscious building regulations. The air between the glass panes works as insulation, the same as in a cavity wall.
Damp-proof course (DPC) under your house floor acts as crude insulation, but invest in laminate wood or carpet for an extra layer of energy-transfer buffering.