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The "editing with a key" is the very easy part! Just put green clip on track above background clip, apply key effect, and move a few sliders for best result.
Truly, the difficult part is in lighting and shooting correctly. If that is done poorly, you can have a difficult if not impossible task ahead of you! Some footage just cannot be saved in post.
My recommendations are these:
1) do web searches for "lighting for green screen" - there are plenty of articles and YouTube videos available. Read, watch, and learn.
2) shoot some sample footage, ideally in same conditions/location the real shoot will take place
3) try keying that sample footage in Premiere, and if you can't get nice edges on the key, change the lighting/shooting setup and do it again until you get it right.
4) when shooting the actual talent, if you have access to the edit computer (laptop?) on site, shoot a clip then test the key in Premiere - if results are great then continue shooting. If you shoot all the footage, then get back to studio later and find out the footage just won't key well, then you may need to reshoot (if possible) and that is best avoided of course.
A few tips I can share:
1) green background does not have to be lit super-bright, just evenly (no hot-spots or shadows). Light background separately from talent.
2) Keep talent like 3 feet or more from backdrop. Too close and green reflection will "spill" onto talent head and shoulders, making keying more difficult
3) record in best quality camera can do. "4:2:2" video is best if camera offers it, since it has more color info = better keying. Most camera formats like "AVCHD" are 4:2:0 which don't work as well. External recorders like Atomos Ninja or BlackMagic Video Assist will record to ProRes 422 and provide much better results than internal recording of most cameras. In any case, if you have options of data rate in camera, choose highest of course. Compression is the enemy when keying.
4) use manual wb and manual focus when shooting, and also adjust exposure manually. Sometimes taking it down a stop or two from auto can help with keying later if subject is bright.
5) test, test, and test some more!
Jeff sort of implied it, but you can download right now some green screen footage from the web, and do a green screen effect and practice so you have at least some experience before you shoot and help with your questions also.
Great point, MyerPJ - just Google free green screen footage and download a few clips to play with to get used to keying in Premiere.
But keep in the mind the download clips will usually be VERY easy keys and not what you will experience the first time you try it, so again test test test with your own footage and leave nothing to chance - the Bank President will not be pleased if he/she has to come back for a re-shoot.