Just as with characters, pickups (aka power-ups) will draw the players' attention. One reason is that pickups are most often highlighted to be clearly visible: Maybe they even rotate or pulsate. Either way, they often stand out visually. Add to this the fact that most players will want to pick them up and you've got a perfect tool to attract players to a location or to pull them along a route. This can also be used well in multiplayer maps where there usually are lots of items around.
In G-Force, we've used this technique to help the player find the way to continue. The environment of many levels requires the player to frequently ascend and descend, however the camera cannot be used to look up or down in regular gameplay.
Because of this, the tops of shelves or tables might not immediately seem like destinations. However, if he sees a pickup rotating on the table, the player is much more likely to investigate. The rotating pickups make the route visible even at the sides of the screen.
This method is used to help the player with his ability to orient himself within the environment. It does so by distinguishing different areas from one another. This helps the player identify them and thus gives him a sense of position in the overall level. This only really makes sense in non-linear worlds such as hub-levels, multiplayer arenas or large open worlds.
Landmarks are immediately visible features of the environment. While within the area the landmark is often in view. This way it can give identity to a location. In smaller maps it could be a statue or maybe a large red truck. In bigger maps it could be a prominent bridge or a skyscraper. As you can imagine, landmarks and the weenies mentioned above can be one and the same object -- to both attract the player to a location and help him identify it.
Unlike the landmark, where there's one dominating feature, using style means that the difference permeates an entire area. It could be a different architectural style, indoor vs. outdoor or plainly and simply a different color through textures, light or post processing effects.
It doesn't matter, as long as the different areas are distinct enough for the player to easily distinguish and remember. A downside is though that you still have to teach the player the relative position of the different locations. It's not really evident to a player standing in a back alley that the little pirate village is right next to the dark woods.
The guide method is building actual guides into the map itself. These guides clearly lead the player along to where he wants to be. This also makes them quite obvious since players need to consciously see and use them. Examples would be signs or colored lines throughout the level. In some cases there are even maps of the level displayed as textures on the wall.
Of course this kind of tool only really makes sense in non-linear environments where there are multiple different places of importance to reach. Especially if the places are complex or there's lots of different ways to get from one to the other. In linear levels there's little need for this.
Valve's Team Fortress 2 is an obvious example for guide signs. The game features complex multiplayer maps that sometimes even change during gameplay. To help the players learn and cope there's a lot of signage throughout the levels.
These signs are clearly visible and generally make it easy for the player to figure out which route to take to get to a certain area. They also fit in well with the visual style and theme without seeming out of place, even though they are clearly huge.
Portal, another Valve game, is a good example of lines. Even though the individual areas aren't too big, the interplay of the different interactive elements can be complex at times. To help here the game visualizes logical connections, such as between a button and a door, by using glowing lines. These are a great help when navigating the environment.
They also have the added bonus that they transmit a lot of other information as well, something that's generally hard to do with immersed navigational tools. These lines also display the states of the different interactive objects (button pressed, energy on...) and their links (button A opens door B).
Lines are also used to great effect in the apple orchard level of the horror game Condemned: Criminal Origins. Playing an FBI investigator, the player has to use his equipment to follow clues such as blood trails. This technique is used throughout the game, but since almost all the levels up to this point are linear, it is of little importance.
In this second-to-last map, however, the player is in an old farmhouse. Here he can freely explore the house, but to make sense of it he has to use his special lamp to light up the four different trails of scrawled writing. Following each of them to their conclusion is required before the player can continue the game. This works really well as the player is unable to fight back while using the light and ends up easily distracted following the writing as it crawls up walls and continues along the ceiling.
The 2008 Prince of Persia video game also makes great use of lines, albeit a very subtle one. In this game, the player's wild acrobatics include walking along walls or climbing up columns. This variety of movements makes it harder to decide what to do when. To help with this the game features scratches and other damage to display the different paths. If there are scratches along a wall then that means that to continue the player has to perform a wall-run. This is a subtle method that works well with the setting but has the problem that once there are different routes the player isn't sure which one to follow.