Use the adverb incessantly to describe an action that continues or repeats without interruption. The neighbor's dog might bark incessantly in the morning, causing you to complain incessantly about the noise.
The word incessantly usually indicates that there's something slightly irritating about whatever is happening. The person sitting next to you at the library might be incessantly drumming her fingers on the table. Your little sister might be incessantly singing Disney songs during a long car ride. On the other hand, incessantly can have a more positive meaning, indicating determination or drive. If you work incessantly to prepare for a big presentation, that’s a good thing!