Everyone kind of has their own way of doing it. What I do...

Take the plant out of the original pot, rinse the leaves off under running water and wash all the dirt from the roots (fertilizers and pesticides are usually in the dirt) Then I clean the pot. Then I plant the plant back in the original moss using substrate out of my tank. I usually leave the plant outside then for a couple of days (though that wont happen in winter), rinse the leaves again, take it out of the pot and plant it in the tank.

I know you can wash the leaves with a bleach solution too, someone should have more advice about that technique.