Trimming (or dressing) is certainly recommended but it’s main use is to remove split ends which makes your hair look healthier. You have a choice to have different styles but they won’t be any longer.
Just as cutting your hair, regularly or really short, doesn’t make it longer, neither does it make it thicker. It could be that this came from the fact that your lawn does thicken up if mowed down short, but you don’t breathe through your hair and the idea doesn’t hold up.
Keeping your Scalp Oiled. While certain machinery does run better when it is kept well oiled, oiling your scalp will not make your hair grow any faster. In fact, excess oil clogs the pours in your scalp and can actually result in hair loss. Keeping your head clean may not stimulate hair growth but it will prevent loss and make your hair look better as well.
One thing that will help though, is hair vitamins