With the skinny elastic I generally cut it to the same length as I do my FOE, they are both really stretchy. I basically heat up both ends of the elastic, and 99% of the time they catch a light and the flame goes out if i blow on it or move it from the candle flame. Anywho, while its still hot I will mush the ends together and try to keep it as straight as I can but normally it's off by a mm or two. I will pinch the 'mushed' bit with my fingers too and warning it is hot but I just push through the little pain and make sure it's stuck properly.
Sorry if that was a little confusing! Then when gluing singed flowers I will glue a circle of felt to the elastic and then glue it to the flower(s). Mind you I haven't got down pat how to have multiple flowers on an elastic headband and have them stay together and not seperate when worn