This is a trick I learnt when I was tired of paying for haircutting. I have long hair (just above my waist) and when I want to trim it, I just get a hair tie and scissors. I lean forward and brush all hair forward and put it in a ponytail. I then pull the hair tie down as far as I want to trim and then cut. It gives a great layered look without the cost. I have only done this with wet hair.