Moving into a house which has been empty for 6-9 months.

[R.O.S.S.I]

All wonderful suggestions thanks everyone, particularly the swingers one!

 

[mattyg]

Id open all windows crank the heating on full and run all taps for 5mins or so.

Grab a brew and check for leaks

 

[b0rn2sk8]

It's likely all of the water system has been drained. Make sure every valve is closed (inc radiators) before turning it on. Have a couple of people on hand to listen out for leaks when you turn it on slowly.

 

[Derek W]

Check under the patio for dead bodies.

 

[Nedved11]

Get some mouse traps place them round the kitchen, this is a good time to find out you got any and you haven't got too much stuff unpacked.

 

[LeeUK]

First things record all meter readings.
Second change all the locks. As already stated, you don't know who still has odd keys. More so if it has been used as a rental property in the past.

 

[Cosimo]

Get some fresh air into the place, make a cup of tea then go through the list you've prepared from the suggestions here..

 

[kingshaun2k]

Christen every room with your Wife/Husband.