Depending on each particular plant's moisture needs, I mixed up the appropriate soil with perlite, vermiculite or peat moss and was ready to add it to the cup.
I held the wick up into the middle of the cup and began putting the soil in. Having the wick run up in the middle of the soil helps it to absorb water more quickly and allows the roots to get to it much faster than if the three strands were separated and on the sides.
After adding a little bit of soil, I separated one string and made a coil in the dirt. I put a little more soil on and made a second coil. I put on a little more and made the third coil and then filled it up the rest of the way. I believe that the coils help to spread out the moisture better than just having them going all the way up the middle.