If you are using a square thong as opposed to a round one, ensure that there are no twists in the neck part and that none are put in when tying the knot. After tying the knot as shown above, tighten evenly. That will take some time, but just work it round and round working the leather one loop at a time until it is tightened and even, and just enough thong is left for the beads. Remember--Practice makes Perfect!
The Diamond Knot was used by Rovers on their thong to designate the completion of a quest. While not neccessary, many Gilwellians have adopted this and tie the diamond knot on their beads to designate completion of their "quest" - namely their Wood Badge -- so here's how it's done.