To provide the best Wi-Fi performance and coverage at your premise, the router should be placed close to the centre of the house on a level flat surface, or fixed on the wall, so the router and all cables connected are out of way, to minimize the possibility of accidental damage caused by people or pets. If practical the router may be placed on top of a tall bookshelf or perhaps on the higher floor if the house is multi-level, etc.
Although Wi-Fi signal will penetrate through standard internal walls the router should never be blocked by other items, especially metal items such as hot water cylinders. Wi-Fi signal will not penetrate through solid metal objects like this and a Wi-Fi dead spot will be noticed behind such solid objects.
The router should never be placed on the floor (even on an upper story), placing the router on the floor not only severely degrades the Wi-Fi performance, it also increases the chance of it been accidentally damaged.
Altering the orientation of the router can sometimes alter the coverage areas, try rotating the router 90 degrees, or standing it up on its end (be careful not to damage or remove the cables and make sure you don't block the air ventilation to the unit).
If the router needs to be installed at one end of the house and/or trial shows the Wi-Fi coverage is not reaching desired areas of the house you should talk with your installer about alternative methods of improving/providing Wi-Fi coverage to the dead spots at your premises.
Our recommended solutions may include adding Power Line Ethernet Extenders or WiFi Range Extenders depending on your situation. If you prefer a DIY solution these types of products are available at most good computer/electronics retailers eg Dick Smith, the products come with easy to follow DIY instructions.