With no training whatsoever, I cut all 3 of my children’s hair for 10 years, but they’re all girls. I started cutting my husband’s hair about a year ago, with clippers and scissors. Tell her to go slow, and cut off way less than you think should be cut off. You can always cut off more, but if it’s too short, you can’t put it back! Keep a large mirror handy, so you can stop and look at it every few minutes. This helped my husband give me ‘directions’, and guided me to the haircut he wanted. Expect it to take far longer than a professional trim, and be patient about it. It helps to be very relaxed (both of you), and to remember it’s only hair…it grows back! Good luck : )