Don't cut the umbilical cord too close to the kitten. Can cause a hernia. And be prepared to shed a tear or two - The 1 time I saw a cat birthing, I got very emotional. 
I removed the bottom drawer from a chest, leaving the gap for her to nest in, with lots of towels in it. She sat on my lap, complaining about her labour pains, until she made her way into her 'den'.
Don't let her eat all the placentas. Let her have a couple, for nutrition. Otherwise her instinct will drive her to eat them all, to hide evidence of giving birth from predators. They're chewy (sorry if TMI), so consuming them uses a lot of energy from an already exhausted cat.
Do be mindful not to let her out until you're able to have her neutered, to avoid another unwanted pregnancy.