The amount of cover and concealment in a game is likely going to be affected greatly by the following factors:
- Classes being represented in your game that have powers and abilities to gain concealment.
- Classes being represented in your game that have powers and abilities that gain considerable benefit from cover and concealment.
- Players in your game that are tactically minded enough to consider the use of cover and concealment.
- A DM that designs encounters with varying environments and interesting details, which can effectively create cover and concealment.
For your own games, make a point to throw in a few details to the environment to help flesh it out and allow for cover. If your players don't pick up on it automatically, run the monsters so that they make use of the cover against players. When your players see monsters using environment to their advantage, it helps drive the point home to them that they can and should follow suit. Put in tables, columns, barrels, rocks, altars, stalactites, or whatever fits the environment.
As a player, try to draw more details out of the DM. Ask him if there are certain details in this room that one might logically find here. Improvise and use something unexpected as cover. Use your teammates as cover, or provide cover to them. It is possible to provide cover, and even superior cover through formations with your teammates.