The biggest problem with WiFi is in networks using the 2.4 gHz frequency. See my article below.
Traditional WiFi, 802.11 b/g/single band n all use the 2.4 gHz band.
802.11 dual band n and the 802.11ac standards use the 5gHz band providing for much higher data transfer rates (up to 1gbit for 802.11ac) but shorter range, not long as gleamy said.
If you have any devices which support the 5gHz frequency, then go ahead and set it up - I strongly urge you to use different SSIDs for the two different bands. If you don't have any 802.11ac or dual band n devices, don't enable the 5 gHz. That will just begin the contention for that frequency in your area needlessly.
Why your WiFi sucks and what to do about it by Tumbleweed_Biff@yahoo.com
The single biggest problem with WiFi connections is contention for the band. Most WiFi (802.11b/g/ and single band n) use the 2.4 gHz band. Not only is this the frequency of all your neighbors, but it is the same frequency as a host of other devices: baby monitors, cordless phones, Bluetooth devices, car alarms, wireless keyboards and mice, wireless speakers on your stereo system, and microwave ovens just start the list. Many of these signals are intermittent making it difficult to identify the culprit, particularly if the offender is a neighbor's device. This situation is substantially worse in apartment and townhouse settings where your neighbors are much closer.
The first thing to do is to make sure you implemented WPA2 encryption/password on your WiFi (not WEP) and look at your DHCP reservation list to make sure you don't have any leeches (unauthorized users).
Things you can do to improve your service:
A) Install antennas, directional or omnidirectional on your router or network card.
B) Counter intuitively … sometimes reducing the TX (broadcast) power on the router can improve your connection by reducing the area covered by the router which makes it less likely to run into other networks or other devices.
C) Increase the TX/broadcast signal of your router. Some routers have a setting which allows you to do this. If yours doesn't, consider upgrading the firmware of your router with DD-WRT or Tomato – assuming your router is compatible.
D) Block signals from other networks/devices: You can do this using something like heavy duty aluminum foil like you find in single use roaster pans you find at the grocery store. Place the foil between your router and any directions where you do not have devices. Example, your router is on the ground floor and you don't have any WiFi devices in the basement – put a layer of the foil under the router. This blocks other signals from getting to your router from that direction and reflects the signal from the router away from where you don't have devices in directions where you do, increasing the signal strength to those areas.
E) Upgrade your devices to dual band N and/or the new 802.11ac standard. Both of those standards use the 5 gHz band for which there is far less contention. The 802.11ac is commonly called Gigabit WiFi because of its near gigabit speeds. Any new devices you purchase should support these standards even if you don't have a router or other device that does so that when you do upgrade your router or other devices your recent purchases are ready to take advantage of it.
F) On older WiFi systems, if your devices support 802.11a then use that if possible. It is slower than N and AC, possibly even g (I forget the exact numbers) but it does operate in the 5 gHz band for which there is far less contention. Even being slower this will be an improvement over 2.4 gHz WiFi if you are having problems.
G) Finally, WiFi should really be your option of last resort rather than your first “go-to”. It is the very nature of WiFi to be unstable particularly given the level of contention from all of the devices trying to use the same frequency. A better solution for most people would be a HomePlug setup. You plug a “modem” into an outlet close to the router with an Ethernet cable from the router to modem. Near the computer, you have another modem plugged into another electrical outlet and an ethernet cable from there to the computer. The wiring of the house is now used to send the signal from A to B. The more modems you have connected, the stronger the signal. You can have multiple connections all in the same house. To add another connection, simply plug in another modem.