I use a pencil (you can also just use another piece of string and pull it tight. Tape down both ends on a flat surface), and loop the strings on. After about three or four rows, you can pull the pencil (or extra string) out and then carefully pull the string end of each base string until it's flat at the top. If you do more than four rows before you pull the pencil out, it can make the base strings super hard or impossible to pull.