The key to a happy pet when it comes to hair trimming is to brush frequently. When your pet's hair is smooth and tangle free, it is very easy and painless to trim. If the hair is knotty and matted, then it can become a much more difficult process! Pin brushes tend to work very well for this, and you can find them pretty cheap online, or at a pet store!
It's also good to train your pet to be brushed while standing. When groomers work, the dog is usually standing, so it's smart to train them to be comfortable in this situation.