There must be a duty. In order for somebody to be "negligent," he must have been obligated to act in a certain way in the first place. Exactly what his "duty" is can be a technical legal question. For example, a store owner has a duty to make his premises safe for those customers who come into his store. But a homeowner may only have a duty to warn a meter-man from the gas company who comes to read the gas meter (warn him of any dangerous conditions in the home). That same homeowner may owe no duty to warn a trespasser he doesn't know about.
Breach of Duty
Once you establish a duty, then you must show that the "negligent" party breached the duty. In other words, he ignored his duty. For example, if a driver has a duty to exercise proper care in the way he operates his motor vehicle, he will considered in breach of that duty if he diverts his eyes from the road while texting his girlfriend from his I-Phone while driving.
The third element of negligent is causation. The breach of duty by the negligent party must have actually caused the injury or the damage suffered by the victim. More specifically, there must be legal cause and proximate cause. (Causation can be very technical, and lawyers frequently argue over these issues).
The fourth element of negligence is damages. The victim must have suffered some damages, some loss, some injury. If a negligent driver crashes into another driver's car, causing no damage to the vehicle and no injury to the other driver, his careless driving would only be "negligence" in the technical sense. Without damages, there would be no remediable case for negligence.