Wireless routers, access points, and adapters send and receive radio wave signals through antennas.  Most routers and access points have external visible antennae, but some are housed internally. Radio waves can be focused like a light bulb, and like light, some materials reduce or stop radio waves. While light focused from several light sources is brighter and makes it easier to see, several antennae in the same area cause interference. This reduces radio signal clarity and effectiveness.

To optimize your wireless range, follow these guidelines:

• Positioning:

  Place the access point in a central location, rather than in a corner. Public Wi-Fi locations usually have Access point (AP) mounted on the wall or ceiling.

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• Minimize obstacles:

  A clear line of sight between AP and the wireless device (laptop, phone, tablet) is ideal. Factors such as number of walls, and wall thickness will affect signal strength. A metal filing cabinet would shield radio waves for example.

  
  

• Avoid interference:

  This refers to other electronic devices using radio waves in the same 2.4G or 5 GigaHertz range. Examples are other wireless routers / AP's in the same room or house. Microwave ovens, when operating could interfere with wireless connectivity close by. 

• Other examples of interference are cell phones, 2.4 GHz cordless phones, and copy machines.
• Interference can also occur when your wireless signal bounces off reflecting objects. Objects can partly or completely absorb signals, reflect them, bend them, or let them pass right through. Metal reflect signals. Water (including the water in human ) absorb signals. Air, wood, and glass tend to let signals pass, but weakened. Plants and the weather can also cause interference.
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• Check signal strength:
  
  
  
  This depends on location. Increasing strength would apply in general, to a country area, but not a city or urban area. If too strong, your neighbours would pick up your wireless network.Power affects how far an antenna radiates. Strength of quarter or half, is fine for most home users.
  Note: The feature Transmit Power Control is only available on certain NETGEAR routers such as the WNDR3800.

• Antennae type:
  
  Antennae do not radiate equally in every direction. Just as a light beam can be focused by a reflector, similarly an antenna signal can be blocked and focused. Because people cannot see radio waves, you must rely on testing to get an idea of where antennas "shine" most brightly. The more powerful and sensitive antennae are on routers, access points, and detachable external antennae, in comparison with antennae on client devices, eg USB dongles. The focus of an antenna is either omni-directional antenna or directional.
  Omni-directional antennas, which are used in most home products, radiate horizontally all around, but are weaker upward or downward. Think of signal strength like a doughnut shape. Where visible, these antennas are usually a rod a few inches long. Following is an example of an omni-directional antenna:A directional antenna(also called a high-gain antenna) radiates strongly in a specific direction. It is usually a flat panel or a dish. These can be  used for point-to-point transmissions, where two antennae are focused directly at each another. These need a line of sight between them, and preferably a large open space around the main beam. Following is a example of a directional antenna:

When you are near the antennae, you receive a signal, even if you are out of the direction of its strongest signals. But at longer distances, you must be in the direction the beam is the most powerful and unobstructed to receive a signal.

For best results, address all the factors that affect your network.