Do a scan of all the wireless channels around you using a tool like...

• WifiInfoView (for Vista, 7, 8) http://www.nirsoft.net/utils/wifi_information_view.html
• WirelessNetView (for XP) http://www.nirsoft.net/utils/wireless_network_view.html
• Wifi Analyzer (for Android) https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer
• inSSIDer (the free/office version was great, but harder to find today)

Note that most tools list the wireless signal as RSSI or dBm (a negative number) in which case a lower number (closest to 0) indicates the better signal.

Then set your wireless router (or wireless AP)...

• to use whatever channel is free (and furthest away from any other used channels)
• if there are no free channels then pick the channel that is the weakest around you
• do not let your router use "auto" for the channel
• setting the wireless to 20Mhz bandwidth may yield better results than 20/40Mhz

You might also benefit from using Google DNS which is 8.8.8.8 and 8.8.4.4 (rather than your ISP's DNS servers which are often lousy) After changing DNS servers you should reboot your router and all computers/devices so the cache is flushed and the new settings are used.

Consider that you might just have a crappy or damaged wireless router. (linksys, netgear, dlink all make "home grade" crap that lasts a few years and/or can only handle very few devices connected simultaneously) Note the count of wireless devices isn't limited to just your own devices, if you are in an area (apartment/townhome/city) with lots of other wireless things in range, all of those other things are also making your router work harder to filter out the "noise"

You could try to firmware upgrade your router (available on the manufacturer's support website)

If the router is extra warm or on top of a heat source (like an amplifier or cable box/modem) move it where it will be cooler. You could try putting a fan near it to keep it cool.

Consider interfering signals nearby that you need to avoid...

• other people's wireless on the same or neighboring channels (someone could have suddenly changed their channel, left their's on "auto" or added another AP)
• baby monitors
• walkie talkies
• microwaves
• cordless phones (use DECT 6.0 cordless phones, which actually use 1.6Ghz to avoid the 2.4Ghz/5Ghz used by wireless networks)
• wireless audio/video senders or security cameras (many of these are extremely noisy 2.4Ghz)
• wireless intercom or doorbells