Southern Dandie Dinmont Terrier Club

Start out by trimming your puppy's nails regularly. Don't wait until they are overlong. This splays out the foot, looks unsightly and can spoil a show puppy's front movement.
You need sharp nail clippers and just take off the curving tip of the nail, where it narrows. Do this as often as every two/ three weeks, depending on how fast they grow,  just taking a fraction off each time.  This won't hurt the puppy and will stop the quick growing to the end of the nail.

If your puppy fusses and wriggles for the first few times get someone to talk to him to distract him while you are cutting - take off as little as possible and be confident and fast! Very often you only need to do front nails, the back ones seem to take care of themselves. Have Quickstop (available at the bigger pet shops) on hand to stop any bleeding in case of accidents, but if the nails routinely bleed you are taking too much off.
Don't forget the dew claws on the inside each of the front legs.