MAC Filtering (or layer 2 address filtering): MAC filtering refers to a security access control method whereby the 48-bit address (also called MAC address) assigned to each network card is used to determine access to the network. MAC addresses are uniquely assigned to each card, so using MAC filtering on a network permits and denies network access to specific devices through the use of blacklists and whitelists. To limit the number of computers to a known few, configuring MAC filtering is a very good option. This is configured on the wireless router and not on the client computers. Any wireless network, SSID needs to be configured on the wireless router. Note that if the router broadcasts SSID, then the clients will automatically learn about the wireless network. If the SSID broadcast is disabled on the router, you need to configure the clients with proper SSID (same as that of the router SSID).
Enable MAC Filtering: MAC limiting the MAC addresses that can access the wireless network, you can prevent unauthorized computers from accessing your wireless network. Note that each MAC address is unique, and hence MAC address filtering can effectively prevent unauthorized computer access. By using MAC filtering, you can allow or disallow certain MAC addresses only. Note that even if the SSID broadcast is turned off, it is possible to access the wireless network if the intruder some how knows the network name.
Changing default SSID: SSID, short for service set identifier, a unique identifier attached to the header of packets sent over a WLAN. The SSID differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same SSID. You can hide the SSID so that it is not broadcast over the wireless network. For encryption, enable WPA2 (or the older versions like WPA). This would provide basic protection for the wireless network. Remember to use difficult to guess password for WPA2.