I used to cut my yorkie's hair myself. I used sccissors and that trimmer comb w/the razor blade sandwiched in the teeth (I've seen them labeled for people and pets and they pretty much look the same). I would have used an electric razor, but he was not going to let me come near him with anything making that kind of noise. But, if your dog is tolerant of it, there are electric razors available spec. for dogs.
Be careful of the the eyes and I try to avoid cutting the whiskers. Also, their private area and any place you know your dog may have injured or is sensitive to. If they don't generally like you poking in their private places, they may not be too happy to see you coming at them with some thing sharp or noisey. You may also want to use a restraint the first couple of times to keep them in place. (if the dog has alot of hair, cut in layers. you can go back and shorten it, but you can't fix it if you start off going too short. Bald spots don't look good on dogs, either.)
In the long run, I think it saves alot of $$$, especially if you just want to get an load of hair off them in the summer and your not too particular about a style.