The first thing you need to do is go out and buy smoke alarms for every room except the bathrooms. You can normally buy multi-packs of alarms to save money. Fit the alarms on the ceiling 30cms away from any walls or light fittings. The smoke flows to the area between the wall and the ceiling last, so hiding them in the corners of the room delays the alarm going off. The same with the ones on the walls; these are the ones that go off after everyone has already died.
Fit smoke alarms before any form of redecorating as a lot of fires occur during and after redecorating. If you took a heat spectrum picture of a live working electric terminal with a loose or not properly secured wire you would see it was red hot. You do a bit of wallpaper stripping, after loosening off an electric socket to strip the wallpaper underneath it. A piece of soggy paper falls down onto this terminal with the loose wire. The paper dries out with the heat of the loose wire terminal and an hour later starts a fire. With the modern fittings on smoke alarms, they twist off easily so that you can paint the ceiling without painting the smoke alarm.
Has the house got adequate insulation? Check the thickness of any batts in the loft in case they are too thin. If there is batts, but not enough thickness chuck some more over the top. Follow the instructions such as putting batts underneath any electrical wires and leaving a gap of 150mm around any recessed light fittings. Getting technical now, the thickness of wires depends on how much heat they can dissipate before they overheat. You could have the right thickness of wire in the ceiling, but sticking a load of insulation on top of it will cause it not to be able to loose enough heat. Combine that with a hot summer’s day and like the song says “the roof, the roof, the roof is on fire”. Strangely enough putting insulation underneath wires does not affect their ability to loose heat much.
If you can get underneath the house consider fitting underfloor insulation. I spoke to someone who had both the walls and ceiling insulated, but they still noticed a difference after getting underfloor insulation. Heat rises, but it also can escape.
If you can get the walls insulated you are onto a winner in winter. The cost is roughly 5K for a brick house and 4K for a weatherboard one. The insulation is pumped in from the outside and the holes are made good afterwards.
Not that you can actually keep the warmth in you can now look at heating the place. If it has got a log or pellet fire, look at getting a form of DVS system that can transfer that intense heat in only one room and put it around the house. Get the summer option fitted as well and you will be cooler on hot days. If there is no real heating consider getting a heat pump or even better a ducted heat pump system so you can warm and cool the whole house. A DVS system is always worth getting as it can dry out a house and moist air is more costly to heat than dry air.
Once you have done all that you can then start thinking about redecorating and gardening.