One of the first methods users employ for more performance is to upgrade antennas. Here is an overview of some of the different types of antennas:

The most common is an omni-directional antenna, which comes with just about every WiFi router or Access Point  on the market. The default SoHo Omni-directional antennas transmits a signal in an even radius. The signal travels equally in all directions in a circular pattern. For best performance, an omni-directional antenna should be level with your WiFi devices. If your space has an open floor plan and no thick walls, for best performance you would place an Access Point with this antenna in the center of the room at desktop level. This type of installation would be appropriate for a SOHO environment; a good quality Wireless-N Router with factory antennas may be all you need.

One of the most common upgrades we see is a stock Wireless-N Router fitted with a high gain omni-directional antenna. Before making such a purchase; it is important to understand if you increase the gain of an omni-directional antenna, you will also flatten out the signal. Assuming the antenna is on a plane, such as the floor, when you enhance the gain, the signal will travels further out, but not as far up.

So, if you have a weak signal on the same floor as the Wireless AP, and all devices are roughly at the same level, a properly placed high gain omni-directional antenna will enable the devices at the perimeter of your space to achieve better connectivity.  It will not create a stronger signal on the floor above or below, however, and may cause weaker connectivity.

A semi-directional antenna transmits a strong signal in one direction in a cone shaped pattern.   They are often placed up against a wall facing into the area to be covered.

High-directional antennas sometimes resemble a small satellite dish or a curved panel.  A high-directional antenna will broadcast a narrow signal pattern; think of flashlight with an adjustable beam.  These antennas are usually employed to transmit a signal over a long distance, and are often used outside.

It is important to remember to select a good quality access point, and then pair the correct antenna with it.  Some access points are more tunable than others; if you are running the stock firmware on your access point, you probably cannot adjust the transmit power, and should take this into account when considering new antennas.