Your tie and your scissors do not really need to be sterilized. The tools are sterilized in hospitals because EVERYTHING is sterilized in hospitals.
If you think about it, it makes sense. Lots of things are going to be touching the cord stump, even if you are careful - diapers, clothing, hands and fingers, and even baby poop, most likely. So if nothing that touches the cord will be sterile, it seems kind of silly to make sure to sterilize the scissors, too. I wouldn't use dirty kitchen scissors that were used to trim fat off of pork chops or anything, but if you are in a pinch, you don't absolutely have to sterilize. To sterilize them, you can use boiling water or you can use a cotton ball soaked in rubbing alcohol to rub the scissors down.
Be sure to use strong scissors. We bought a new pair for ours and they were kind of dinky. Cutting through the umbilical cord was like trying to cut through a bicycle tire. I tossed the little scissors over my shoulder and had DH bring me the kitchen scissors
You can use dental floss to tie the cord, but I have heard of a lot of moms having problem with it cutting through the umbilical cord when tied tight and it can bleed at the cut site. It's best to use something thicker if you have it. My midwives (I had them only for my prenatal care, not the birth) gave me a piece of hemp twine to use. You can also use a piece of ribbon or a brand-new shoelace. Braided yarn is also good.
Tie the cord one inch from baby and be sure you tie it super ultra tight. Put three knots in it so it doesn't loosen as baby wiggles around all day. I love the goldenseal powder. You can put it on immediately after. It's also great to use if you have a tear. It healed mine splendidly. It does sting, though, so be sure not to use it anywhere else on baby. Also, it stains like mad, so don't put any clothes that you really love on baby until you stop using it.