I'm running 4e but I think this applies everywhere.
I want to use terrain more often in my fights. My best fights are the ones that revolve around interesting terrain. The problem is that I don't grok what makes terrain interesting. My usual method is to throw in as much terrain as I can and hope some novel tactics emerge. That or ignore terrain altogether because it takes me a while to come up with.
Once I have terrain, I don't really know how to make use of it. I mean, putting archers out of reach is about the best I can do. I'd like to make areas that have more goals than 'clobber the other side,' or 'get to the archers, then clobber the other side,' because I think new tactics will emerge from other goals. But unless the plot demands it, I can't come up with anything else.
Best Answer
I think two other comments (here and here) do a good job of answering your questions; I am grappling with the same challenge of late. I want dynamic encounters that test characters beyond just run up and hit the baddie.
When tinkering with an encounter I always look at it from the perspective of . . . what other ways can the players use their characters to solve the challenge.
That statue sitting in the middle of the chamber, why not make it somewhat old and easily knocked over so that it will land on the enemy or provide cover or whatever. Athletics feels like the right skill there.
Or perhaps you can insert a point of elevation that no one has seized, but to get there the archer will need to scale a narrow ledge and expose himself to enemy fire. But once there he will have cover and visibility to most of the enemy.
And if the players don't get the idea, then have their foes provide an education. "Out of the corner of your eye you see a goblin making his way up a tree, presumedly to find a perch from which he can rain arrows down on you." What the enemy can do, so can the party. In addition, why not a passive insight or perception?