Tips for data security

Question every request for personal details when making a purchase, joining an internet forum, filling in an insurance or credit application. Refuse to provide any details you see no valid reason for. Do not confirm your identity, address or household to call centers that get through blocks on your phone, just hang up. Don't take part in "surveys", don't use postal votes. Don't enter "competitions" which require name and address or family circumstances.
Put unopened junk mail back into letter boxes, buy and use a shredder, limit the number of "loyalty cards".
Ask your bank and insurance company what use they make of your details (the latter won't reply).