The first condition is that you shall not charge for the sample. It must be genuinely free and you cannot receive anything in return for it.
The second condition is that the sample must be an example of one of your products and you must give it for a genuine business reason. Advertising your products to the public would be a genuine business reason, but giving a sample as a present for personal reasons would not.
Note that you do not have to account for VAT if these are also free samples that you received from your supplier.