I'm not a professional groomer, but I don't fancy the typical 'puppy cut' by groomers, so this is what I do...
I have Scottie stand on a box covered with a big piece of paper - paper for easy clean up. Then I comb out the hair. Then I cut a straight line from the hind leg to the front leg, so that the hair is hanging straight to their belly. And then the same on the other side. I also trim a little bit in the area between the hind legs and the area between the front legs.
Then for the face, I grab the hair below his chin and trim straight across, as short or as long as I want to keep it. I trim the sides of his face too, but I think I need a diagram - can't really describe it.
It wasn't hard for me to get started. If you hold their face and they're willing to stand still, you're set. Both Scottie and Casie love it. They always look like they're enjoying themselves as if they were being pampered
If you struggle a bit at first, just do a little at a time - different sections on different days. Hair always grows back. But if you do a little at a time, the pups will gradually get used to it. And then you can take your time with the trimming, eyeballing it, kind of like the art of trimming a bonsai tree. If you're afraid of handling the pup with scissors, try using children scissors - they're less intimidating.
Amazon.com : Westcott Classic Kids Scissors,... I use something like these on their paws and ears.