Step 2: Preparing the Yarn and Math
Find a moderately sized object that won't snag yarn - this is the box I keep my knitting supplies in. It's about 12x18x4 inches. I wrapped 2 skeins of Sugar 'n Cream yarn around it, if you're working with more yarn you'll need a larger object (and obviously, if you have a warping board use it!) Cut about 2 feet of tie up string. Start wrapping your yarn around the box keeping the rows even and not overlapped. Weave the tie up string between around every 5 wraps. Keep going until you've wrapped all of the yarn around your object.
When all the yarn is wrapped start tying it into groups. I tied mine into 10 strand bundles. Two things go into this decision. First, the number of loops is how much you might have to untangle at a time. Second, each group is going to be a shade in the ombre. More groups will result in a more subtle color variation. Tie them tightly enough to keep the string together, but not as tight as you can because that can prevent the dye from getting to the yarn.
Count the number of groups you have tied. My dye pack said to dye the yarn for one hour. Subtract the groups you're leaving undyed and the number of groups you want at maximum color (I had 29 groups, I left 6 white, and dyed 3 to maximum color, leaving 20 groups.) Divide 60 minutes by the number of remaining groups - this will give you how many minutes you dye each group before adding the next. I dropped in the next section every 3 minutes.
When all of the groups are tied once, start sliding them off of the box and tying them again at about the center of the loops. If your loops are very large you might want more ties.
Put any yarn you don't want dyed into a plastic bag and zip it up as well as you can. This is to prevent accidents.