How to help yourself
Encrypt it! Encryption converts your information into a code which can only be ‘understood' by authorised people or devices. WPA (WiFi Protected Access) or WPA2 are considered the best and modern device should support this. Older devices may need to use WEP however whilst this is better than no encryption at all, it's not considered particularly secure..
Set a password: Set up a strong password at the point of access to the wireless network to prevent those who aren't authorised to, accessing your network.
One point of entry: By using access control you can restrict who can get onto your wireless network. In the example of a home wireless network, an access point is the ‘gate' through which all the devices in your household access the network. Using this method is safer as it allows you to set a password to restrict access by computer or device so only those you know can get on your network. Refer to the instructions for your wireless router for details as to how to do this.
Set up firewalls: Make sure that all the devices that can access your WiFi network have a desktop firewall.
Stick with the familiar. If you're using a hotspot, stick to those provided by trusted commercial operators like BT OpenZone or T-Mobile.
Access points only! Try and restrict your connections to access points rather than ad-hoc connections and use encryption (preferably WPA, but failing that WEP).
Use protection! Make sure the security on your computer or device is up to date especially where available, your firewall.
What are you doing?! Think about what you're actually doing on these WiFi networks - avoid transmitting sensitive information (i.e. like accessing your bank account). If you have to carry out these types of transactions make sure you're using a secure webpage (these start https:// and have the padlock symbol in the address bar).