Visual hints can be key to having the player focus on the task at hand. Having smoothe gameplay is essential. When a player is lost for 30 minutes something went wrong and the gameplay is now interrupted. Sometimes if them game is good a player will sit there and try and beat it. But most of the time the player will play another game that's less confusing.
An environment change can be used as a visual hint. For example when i was walking to class and i took a shortcut. But the question is how did i know it was a shortcut? Because so many people where taking the same path the grass died and the dirt became visable. This let me know it was a viable option to take. We can use this in games by breaking up the environment with dirt paths or a visual cue that tells the player "you can go this way as well".
Another visual hint can be using cracked objects. If a player sees a normal object a few times and a cracked vesion of that object they will assume it is destructable. Don't get me wrong this is not always the case, but 9 times out of 10 the player is expecting a new expierence to come forth when encountering a cracked object. In most games a this mechanic is used with a chracter that can break through the object. The character can have an attack ranging from a simple headbut to a ferocious choulder charge.
Lights can also be used as a visual hint. For example if i was in a dark room and there was a light in the distance I would flock to that light because everyone knows bad things don't spawn near light. Lighting up an area can let the player know " Hey you can go to this area ".
Music is not visual but it too can be used to guide the player. For example I could make a game where if a player heres a flute melody they would be close to burried treasure. Or if they here drum beats they would be close to enmies.