-- Take care of air barriers, ventilation and vapour barriers before insulating. Check out these three topics in the Search Tab above.
-- Don't block the eave vents with insulation.
-- Do cover the top of the outside wall.
-- Don't put plastic foam on top of porous insulations (batts, loose fill) as it can trap humidity. The reverse is OK.
-- Don't put heavy insulations (loose fill) on top of compressible insulations (batts, lighter loose fill), as this will crush them and reduce their insulating value. The reverse is OK.
-- Don't allow the wind to blow loose fill around. Cover it with batts or a house wrap like Tyvek.
-- Lay the batts across the joists to insulate the wood. Lay the batts tightly together and don't let their joints fall above wooden joists or there will be thermal short circuits.
-- Heavily insulate all exhaust ducts and plumbing vent pipes to minimize inside condensation. Removing ducts from the attic is the only way to stop condensation inside the ducts.
-- Do not seal or insulate recessed light fixtures as this could cause a fire. Even covered protective boxes are no longer legal -- remove them. The only recessed light fixtures that can be used in an insulated roof space are ones certified safe for the heat trapped by insulation (IC) and ones that have all the holes in the can sealed off air tight by the manufacturer (and don't forget the "air tight ready" ceiling gasket that completes the sealing process). The heat of the lamp is a fire hazard, and it works like a pump to move warm moist air into the attic. Fire safe and air-tight or remove recessed light fixtures.
-- Do not insulate within 150mm (6 in.) of any metal chimney, but do seal the cracks around it.