Lilies consist of six petals per flower, always arranged the same way on the stem regardless of the type of lily.
To start setting the petals run a small line of glue around the bottom edge of your thread stamens. Pick up the pointed end of a lily petal with your tweezers and press the cup shaped, rounded base of the petal into the bottom of your glue line, pulling the petal up to the base of the stamens and catching it against the stem in the glue. Set three petals evenly around the stem this way.
The second row of petals overlaps the first, with the bases on the same line. Use a pin or a toothpick to place a small bead of glue at base in between each of your first three petals. Set a second row of three petals around the base of your flower, making sure each new petal overlaps half of each of two petals in the row below it. You shouldn't see the base of your thread stamens. Set the flower aside to dry (Insert the stem it into a scrap of styrofoam packing, dry florist's foam or modelling clay to hold it.)
When the flower is completely dry, gently take your tweezers and pull the petals into an open or closed flower shape to suit your needs. Take a bit of the green paint you used for the stems and paint the stem where it meets the base of the petals. Don't paint over the petals unless you have to do so in order to make the base of the flower even with the other petals.