I can see that most people have suggested that the house is visited by a neighbour or relative who lives nearby daily to do the lights and curtains for you. Or if there is no one to trust leave a low wattage bulb on all the time in the hall.
There are two sorts of burglars. Opportunity and Stalker. The first, if they know you will be away will take the chance that there might be something to steal, the second knows you have and will be watching the house for other signs.
They could be checking your bin to see if it is empty, that nothing extra has been added recently. I put mine in the Garage.
If you usually park the car somewhere visible and it is not there, that is another sign. The grass growing longer than you normally allow or the planters are not being deadheaded. So give some thought to that sort of thing. Thoroughly mow and trim just before you leave.
If you have valuables in the home it is wise to protect them in your absence by hiding them. Take photos of them to keep too, so that in the worst case, you can show to the police what was taken. It also helps if you need to make an insurance claim.
When you have to tell some one you do not know, that you are going on holiday, the taxi driver perhaps who is taking you to the airport or even if you are telling your hairdresser and some one can over hear. Add that your sister or daughter (you choose who) is staying over for the time. To look after pets perhaps. Wave to nobody at the window from the taxi as you leave the house.
Water can cause a lot of damage if there is a leak so turn it off.
If you are going away in winter set the heating to come on for an hour or so each day to keep the place warm.
Fires can happen. You should turn off and unplug every non-essential appliance. If you are considering turning off all the electricity then you can not have a light on, and the freezer better be empty, you may not be able to keep the heating on. Your burglar alarm wont work either
Throw out, freeze or compost any food which may rot and get smelly.
Close all the internal doors, spray a little fly spray into the room as you go. Pour some disinfectant or bleach into plugholes in sinks, washbasins, baths, showers and the lavatory.
You could also leave the telephone off the hook so if any one calls it always sounds engaged. Try and answer e-mails whist away. Some one could e-mail you to check if you are replying. So watch what you say to any one you are unsure of.
Hide the keys to the car and parts of the home which are locked. If you keep a spare set of keys for another person, with their name on the key ring, your burglar may be able to get into their house too. Hide any banking details credit debit cards you are not taking with you.
Put your name and address on a label inside the lid of your suitcase with the number of some one who can be reached whilst you are away. if the cases are lost, then you can be re-united with them quicker by doing this.
Keep a photo copy of your passport. Even scan and keep a copy of it on an e-mail you send to your self, this can be invaluable if it gets lost or stolen whilst you are abroad. Travellers cheques too. The details can be retrieved by you anywhere in the world.
When packing suitcases always keep a change of clothes in another persons case, if you can. Bags can be delayed when flying but it is unusual for an entire party to loose all their cases. Best to pack half and half if you are a couple, you can probably manage with half your stuff anyway.