With a slight Taper being longer towards the outside, I always section off the amount of hair to become bangs, moisten, comb straight down and gather together to make a V. Holding, cut as straight as possible while looking in the mirror. Always cut longer and work up rather than too short to start. Good news....hair grows out..lol
Don't wet your bangs and cut them. Hair when wet is longer and it will shrink once it dries. Also hair has elasticity and will spring back shorter than expected. Don't use a narrow tooth comb as that will pull the hair too taut and will further complicate the trimming of bangs. Don't use just any scissors, hair shears are designed for cutting hair. Finally, go to a professional and have them trim your bangs. It shouldn't cost more than $5 to $10 for just a bang trim. A hairstylist might charge you less in the hopes of getting you as a client for other trims or services down the road. If they charge you for a full haircut walk out. Don't go to a hack shop (i.e. Supercuts, Cost Cutters, Fantastic Sams, etc.) they may have good folks working there but most are not. DON'T go to a cosmetology school for this either. They are cheap but they are still learning and they are learning to pass the state test. I know as I have been a licensed cosmetologist in CA for 27 years.
get a "rattail" comb or whatever they are called, or a normal comb. comb your bangs. gather a small section. then trim it. once that is trimmed grab alittle on the cut section and grabbed a none cut section then you can tell how short you have already trimmed it. (if you want them even)
i'd say dont use scissors because you might make a mistake you know.and scissors leave an ''even cut'' But use a Razor.when i cut my hair at a salon for my bangs they use a razor.its amazing be cause it doesnt cut alot.you wont worry if you mess up because ti gives it a unique and a texture look.and when you cut with scissors you can notice it.razors know how to blend a cut with hair.and its soothing too.