Not in a "Character" on Camera? Causes, Result and Solution

Symptoms

1. Forgetting your lines after the director says "Action"
2. Not being in a "character" in a particular shot or in the entire scene
3. The camera catches your gaze, wandering while your Co actor is talking to you
4. Lack of necessary expressions while delivering your dialog
5. Lack of required energy level in your performance
6. Wrong movements (not hitting the mark while walking)
7. Not using the props properly
8. Getting stuck with speech, a word or speed

Causes

• Lack of preparation (The reason could also be getting script/lines on the set)
• Getting distracted with the activities on a set, which is always chaotic before a loud "quite" or "silence"
• Gossiping with Co actors or crew before or after your shot when you may be having more shots remaining
• Using your cell phone often

Consequences

1. Wandering mind leading to lack of concentration and focus
2. Poor performance
3. Multiple retakes of a shot annoying director, producer, DP and crew members
4. Earning a bad name of a "poor actor" 
5. Bad publicity and losing opportunities
6. Shattered dreams of becoming a "Star"

Treatment (Solution)

• Practice meditation 
• You have to give yourself strong auto suggestions, repeatedly
• Practice concentration regularly by focusing your attention on a single object for as long as you can (lamp, table, pan etc.)

When distractions occur:

• Take a deep breath, hold for 5 seconds and release it very slowly. Repeat this at least 5 times
• Order your mind by saying "stop" or "stop wondering", Shake your head vigorously for a second and say again "back into", when you notice your mind wandering
• Pinch your arm or thigh hard
• Immediately shift your posture to an awkward one 
• Say to yourself repeatedly "I'm so and so" (Character)
• Say to yourself positive things like "I can do it", "I will do it" or "I'm good, yes I'm good" to bring back your concentration
• While on set avoid as far as possible what I have mentioned under "Causes". After all, your career is more important than gossiping, phoning or flirt around. 
• Speak  only what is relevant and required as a courtesy, on the set. 

(However, this does not mean you do not clarify your doubts with a director or cameraman. For your flawless performance, you must ASK)
If you practice the above regularly, you will tune your mental instrument so well that over a period of time, you will learn to be in a character instantly, irrespective of distractions