depends on the plant ... if i just get a cutting of an epiphyte or something, i usually just sort of set it on top of some moist sphagnum and see how it does ... bromeliads i stick the stolon into the clay on the background and sometimes add additional supports made from toothpicks or those plastic coated paperclips.
potted plants that i'm moving into a viv i like to rinse them really well because one time i got a snail that rode in on one and ate a bunch of stuff. luckily there seems to only have been one and no eggs. as for the soil, i've been told that chemicals like fertilizers and such can cause problems for frogs, so I rinse the roots really well and make sure i get all the little white balls off of them before i put them in. then i just sort of scoop some of the top layers aside and stick them in.