I have a new lady crush. She's got platinum blonde hair and a russian accent that makes anything she says sound sultry. You WANT to listen. Not to mention that the styles she comes up with are to-die-for. If you have hair, and like looking nice ...get you to her Youtube channel.
As for trimming hair? Lilith goes over the whole thing in beautiful detail. Things to remember? Do it every two months. Use sharp hair-specific scissors so as not to cause more damage to your hair. And keep the trim to a small amount. You're only after the dead and split ends here.
And don't forget! Write on your calendar so in two months you don't forget. :)
I would like to add, that if you have very straight and fine hair like myself you might like to try some soft layers. This video by Rosebud143 shows how you can achieve this. I've done it with my own hair and liked the results.