To chroma key, or green screen, you need to have a wall of one color that easily shows up in film. The color should not blend with your body or your clothing. Videographers use bright green often because people typically do not wear the color. A solid, flat wall makes green screening easier. A wall with bumps or folds can alter the brightness and hues of the colors and may not be completely removed in postproduction.
The green screen should be in a room with enough lighting to illuminate the entire screen and the people in the video. The screen needs to be lit evenly. If not, the screen will appear to be various shades of the color you chose and it may not disappear fully as filming continues. Also, do not film light directly in front of you in order to prevent shadows, which will change the color of the wall as well. Light either from above or from the sides.
Film the video as you normally would with a physical background. If the person in the film interacts with objects that will be added later, map the scene out carefully beforehand to prevent misdirection and awkward keying in postproduction.
If you plan on using a green screen, you need to have editing software that allows you to key out the color of your choosing. This software could be Apple's Final Cut, Adobe's Premiere or other similar software. Select the "Chroma Key" or "Keying" option. You will be prompted to select the color you wish to key out of the video. Select the color that matches the background of your video. You then have the ability to insert a picture or another movie as background.