Meet with the other production personnel to review the script and specific lighting concerns. Find out what tone they are looking for in general and within specific sequences as well as what kind of equipment you will have at your disposal.
Make a detailed lighting plan for each shot in the film using the script and notes from the meeting. Group by light set-ups rather than shots or scenes. Make a list of equipment you will need and when you will need it.
Gather or secure the lighting equipment. Depending on the budget this could mean renting lights, using a studio's home set-up or crafting cheaper DIY solutions that will guarantee quality results.
Arrive early on set. Explain the lighting plan to all personnel.
Turn the main lights of the room you are working in off and begin the individual lighting set-up. Media Ed.org recommends you "start at the back and work forwards, adjusting distances and angles as you go."
Use the standard "Three Point Lighting" technique. This includes a backlight, which is behind the actor or subject in the scene and separates them from the background with a rim effect; key light, a strong but diffused light shinning on the subject and usually placed to one side of the camera that is the tallest and brightest light in the set-up; and fill light, a light dimmer than the key that is meant to fill in the strong shadows on one side of the subject created by the key. The fill light is placed at an angle across from the key so that the three lights together form a "T."
Make sure there are some shadows in the frame. Shadows are necessary to create depth of field and provide a sense of spatial relations.
White balance the camera before each new set-up to accommodate different light temperatures in the scene that affect the way color appears in the final product. White balancing makes sure white in the film will look to same as white does to our eyes, and so on with the other colors. Cameras can automatically white balance or be set to manual white balance, where you can zoom in on a purely white piece of paper and adjust the settings accordingly.
Take photographs with a digital camera to see how the lit scene will actually look on film. You can examine the photos and see what alterations need to be made.