Light and sound

Light and sound have a powerful effect on the player. Aside from making the world feel more realistic players will be guided by these elements.

Light
Lighting a map correctly has become an artform in itself these days. You could spend months tweaking lighting to get the best results.
This guide is primarily focussed on gameplay so we'll skip all the asthetic details. Its enough to say thay players will be drawn to the light. So if you have 2 routes and one of them is not the way the player should be heading, make it darker.
Light can also be used to highlight important areas of an area. Got a handle or button that the player needs to interact with? Light it up.
I would also point out here that players are naturally drawn to more natural forms of light. Between an indoor lit area and an outdoor area the player will generally want to head toward the outdoors. Dont ask me why... human nature or something.
These elements of human nature can be a very useful tool sometimes...

Sound
Sound can build a world beyond your map and create the illusion of many things, what the ear hears, the brain builds into the overall environment. Sound can also be a really handy tool to tip the player off of an upcoming danger or an important element of an area. The more you want a player to focus on something the more noise or more regular noise it should make.