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Tie the rest of the hair back into a low ponytail. Make sure that the only hair out of the ponytail is either the hair that you will cut into bangs. This means that if you want your bangs to blend into the rest of your hair, cut them long enough so that all of your bangs are the length of that longest hair. You can always cut more. Comb your bangs horizontally so that they lie flat against your face. Decide how long you want your bangs to be. Remember that you can always cut them shorter, but you cannot add back hair that you cut off. Use your nondominant hand. Make sure that the hair is even and pulled taut.

Summary:
Comb the bang hair forward. Cut horizontally to the longest possible length that you want your bangs to have. Hold bangs flat against your face with a comb. Hold bangs between your middle and index fingers.