If the claws are white, clip to just before the quick (red blood vessle).
If the claws are black, just clip the tip off, leave it a week or two then clip another couple of mm. The quick will gradually recede so - theoretically - you will never cut it.
For the dogs comfort, bend the leg 'backwards' if you get what I mean - naturally bend the joint. Don't lift the paw up to the front. Perhaps you could google for an instructional video as it is hard to describe sorry
Might also be an idea to get a professional groomer to show you first time. Not normally very expensive - £10 to £15. Takes five minutes so a bit of a rip off lol.
Even though doggy is placid, give a scrummy treat afterwards and do it regularly so dog remains co-operative.
It isn't hard once you get the hang of it.