To trim or cut your own bangs, invest in a pair of quality haircutting shears and a comb. Trimming existing bangs is the simplest. Style your hair as you would on a normal day, making sure that your hair is completely dry before cutting. Section out your bangs, and clip the rest of the hair back. Pull your bangs in front of your face, and cut perpendicular into the hair. Only trim a small amount at a time.
If you do not have bangs already, cutting your own bangs is a little more complicated. First, you must form the starting base for your bangs. To do this, create a triangular part, and pull the hair within the triangle to the front. This section of hair forms your new bangs. You can cut your hair wet, but remember that it dries shorter than it looks when wet.
Next, brush the bangs either straight down or to the opposite side of the head. Comb the hair straight down and cutting across as you would when trimming to result in straight bangs. To cut side-swept bangs, comb the hair to the opposite side, and twist it towards the back of the head. Cut parallel to the part. Sweep your new bangs over to their normal side, and style as desired.