I just planted 2 cuttings into my nursery bed this week which I kept when I pruned the parent bush last year. I just stuck the cuttings into pots with compost and perlite ( think thats what the white stuff that retains moisture is called) and put in in my coldframe over winter. 2 of the three kept survived.

Cut (with sharp secateurs or knife) just below a bud near the base of the plant, count up for three buds and cut just above this one, so that you have a stick with three buds on and just push it a couple of inches into the ground and, bless my soul, next year you'll have a new buddleia shrub. I usually do three or four to allow for failures, but I find they hardly ever do.