Chroma keying requires evenly lit, flat backgrounds without shadows or creases. Subjects should be far from the backdrop and avoid wearing the same color or anything shiny. When filming, use static shots and smooth down hair. In FCP, place the background in video 1 and clip in 2. Add chroma keyer filter to the clip, select the backdrop color with the eyedropper, then refine by shift-clicking remaining areas of that color.