Trimming around his muzzle may be a bit challenging, but it needs to be done. The most important thing to remember is that your pup will pick up on your nervousness so be calm and patient with him and you both will do just fine.
The last thing your dog wants is hair getting in his nose, his eyes, or his mouth every time he eats or drinks. Imagine how you would feel if it was you. Of course, you know your pup is not going to be so happy with the idea of watching you with shears or clippers in your hand that close to his face. But, if you give him time to get used to the tools and being trimmed, it won't take long before trusts you.
Long before you break out the shears or clippers, take a few minutes to research what the average dog in your dog's breed looks like. This will help you to cut your pup's hair and muzzle properly and not leave him with an embarrassing haircut he will not be happy with. Of course, in time the hair will grow out and your pup will forgive you.