Make sure they have lots of humidity, I use a dome with the small individual slots and I use flexible cups so I can take em out 1 by 1 without disturbing the others. I use Olivias cloning solution diluted in distiled water because it has a light feed and rooting hormone. In my cups I use 50% vermiculite / 50% perlite. I keep em well wetted with the solution per directions on bottle, and I spray the leaves and the top of dome lightly 1-2 times per day for the 1st few days than I back off on this eventually to once per day lightly, I never totally stop misting though. Usually within 5-7 days they have decent roots, but this can depend on strain. My success is basically 100% with this method, I dont even have leaves droop. I know people who use only water and have good results as well.
Make your cut just below a leafnode, maybe 1/2 inch, at an angle and stick into the wetted mix described above. Keep the dome near light but not in the full light, I use flouresents for these tasks and I have mine on 24 hours. Some people cut the leaves in half so they shorter stubs after they take the cut so theres less for the clone to support.
I also use a clean razor blade new out of package and keep my hands very clean, overly cafefull, probobly, but its the way I do it.