It is acceptable to use scissors to trim the hair between the toes. You could just take scissors and trim your dog, but you would be doing him no favor and not helping his coat to improve. Take the time to pluck the hair. Dogs mind having the shoulders and back done less than almost any other part of their body. A little gentle plucking around the anal area is also important.
Long hairs tend to get dirty and make the dog uncomfortable.
Gentle use of the dull knife will preserve the cowlicks, but get rid of excess hair. You can make the skin the area taut by pulling upwards on the dog's tail. Use scissors to trim around the penile sheath, and remove the urine-soaked hair. If you are not experienced, you may want to ask someone to hold your dog for you at this time. The same applies for the area around the nipples, before she whelps.