Step one:
Out of the box your your wireless device shall broadcast itself as far as possible. Its there and it want to be found as easily as possible. First thing you want to do is change your Service Set Identifier (SSID). Anyone with a computer can find out default SSID. You may wonder why you need to do this. The answer is that Each wireless network node needs to be configured with the SSID name. The SSID is sent out in the header of each packet broadcast in the area. Data packets that lack the correct SSID will be rejected.
Step two:
Turn off the damn broadcasting of your SSID.
Step three:
Enable MAC address filtering. This will limit access to your wireless network based on the address on of the units NIC card. Basically your creating a white list containing accepted MAC addresses.
Step four:
Have the most up to date data encyption WPA2. Rather long explaination. Just know that its the most secure.
Step five:
When setting a password apply the same idea you would use for any other password. Upper and lowercase numbers and special charactors minimum of 8 chars.