*Always changing floor height when I wanted to change floor textures. *Using special border textures between different wall segments and doorways. *Being strict about texture alignment. *Conscious use of contrast everywhere in a level between light and dark areas, cramped and open areas. *Making sure that if a player could see outside that they should be able to somehow get there. *Being strict about designing several secret areas on every level. *Making my levels flow so the player will revisit areas several times so they will better understand the 3D *space of the level. *Creating easily recognizable landmarks in several places for easier navigation.