In general, you must prove the following four elements:
The person who injured you owed you a duty of care;
The person who injured you failed to meet his duty of care (by driving while intoxicated, for example, or by prescribing you the wrong medication);
You suffered tangible harm; and
The failure to meet the duty of care played a substantial role in causing the harm that you suffered.
Note that the person who injured you might not be the defendant. You might choose to sue the employer of the person who injured you, for example, if the accident that injured you happened while the offending employee was on duty.