During a game experience, players generally won't have any reason to quit the game, unless they experience a moment of frustration. If players get lost or can't figure out what to do next, it can be quite a frustrating experience. As level designers, we want to avoid this at all cost by guiding players throughout the game by using player psychology.
There is a 180-degree rule in cinematography that states that two characters in a scene should maintain the same left/right relationship to one another. When the camera passes over the invisible axis connecting the two subjects, it is called crossing the line and the shot becomes what is called a reverse angle.
Video games might be a bit different, but it's a good rule to keep in mind when designing complex game levels. Levels that contain multiple rooms connected to multiple paths can be quite confusing. Portals that teleport players such as the ones found in the multiplayer maps of Quake Champions can be confusing. Symmetrical maps can easily be confusing if the visuals of each side isn't completely different and sometimes to just use different colors isn't enough.
When players are moving through a game level, they are always looking for the next thing to do. Level designers can strategically place pickups (coins, potions, weapons, etc.) on the map to help redirect the players during their adventure. Plus, pickups are powerful tools to add replayability to a level by encouraging players to explore their environments.
Level designers can also redirect players by using objectives and placing interactive elements such as levers, buttons, puzzles, jump pads, portals, etc.
And to place enemies on a map is still to this day one of the most effective way to redirect players during their game experience, because players always associate enemies with the main path.
By using shapes, repetition and placing objects in specific ways, level designers can use the world geometry to create invisible lines and curves that can be used to help redirect players during their adventure.
Level designers can use colors as a special language to highlight the main path. Such colors can be assigned to climbing routes, objects required to solve puzzles, etc.
To help separate the interactive elements from the rest of the environment, game developers often create their own visual language by creating unique gameplay props that will be re-used during the entire game.
Level designers and artist heavily use lighting to show the path to the user or highlight important areas or items.
The term "preview" here is being used to describe a window that allows the player to view another section of the map. This technique is used to make the level feel bigger, more connected and also to show hidden items.
To save production time, game studios tend to create a small library of game assets that will be re-used to build 3D environments. This is an excellent way to build a visual theme, however all the different areas of the level might look a bit too similar. To break this, designers and artists will organize the different sections differently and create unique landmark areas that are easy to identify and recognize. In certain cases, visual landmarks can be seen from afar (ex: Clocktower) to help players navigate through large environments.
Top help navigation, game developers can add extra hints in the environment.