RotMG is a permadeath game, so it should come as no surprise that staying alive is good. However, some people have the unfortunate luck to be instantly killed, and others are plain dumb. Try to avoid these deaths.
1. Instant Death
As you can see here, a user by the name of "WobbyTubby" has succumbed to the grasp of death in a dungeon. How was this poor fellow brutally murdered? Instant Death. One of the 3 bosses in this dungeon jumped from behind him while spraying a swarm of bullets that slowed his movement. Alas, he had no time to react. The poor fellow was instantly shotgunned by a flurry of status effect inducing bullets.
This kind of death is one of the main issues in RotMG. Sometimes, it is not skill that keeps you alive, but luck. Many bosses have movement that is way too fast, and some randomly shoot out massive amounts of shots. Many people have been begging for a solution. Unfortunately, there isn't a solution. There is no possible way to make a boss less likely to instantly kill a character without making it arbitrarily easier. Players must simply take the precautions that can improve their chances. If they don't, it is mostly their fault.
2. Imbecilic and Utterly Foolish Deaths
As you can see in this image, two players died attempting the same risky behavior. In this particular run of the dungeon, the boss had already died, yet the 2 players still managed to kill themselves. They were attempting to see if they could stand on a platform in the middle of the most damaging liquid in the game. The liquid does over 150 damage per second, and the faster you move, the faster you take damage. There is no point risking your character to find out something that can never be used. Simply stay away from activities involving potential danger.
I'll revive my RotMG dungeons guide soon. Keep these deaths in mind while reading them!