Make sure it has cheque garuantee on the back... Says someting like Garuanteed £150/£300, etc.

Write down the numbers found on the card on the back of the cheque. I also take the expiery date, and write that down too.

Make sure you see them sign the cheque (don't accept a cheque already signed), and compare it with the signature on the card.

Make sure the cheque and the card is from the same person. (Same name)

And off you go! Good luck!