So its a box with a bunch of scattered stuff.
As far as DMs go a rule of thumb is to actually have terrain. Seek inspiration from games like Doom and TF2 as to how a DM should be built.
Case Study: Team Fortress 2 Arena_Ravine

Key
Color | is | What |
Red | is | Random Object |
Teal | is | Detail |
Blue | is | Upper Area |
Green | is | Lower Area |
Purple | is | Structure |
Lets examine:
First, we have the
Upper Area, this area is large and flat. Large, flat and plain areas should be avoided, so we have our
Random Object. The
Random Object obstructs vision and helps to eliminate the flatness. This
Upper Area borders the
Lower Area via a ramp, and the
Structure via a bridge.
The
Lower Area provides our elevation difference-- one elevation throughout leads to large flat plains. Notice how the
Upper Area uses
Random Objects to provide it's cover and obstructions, but the
Lower Area uses the
Structures that are built into it.
So, there are two
Upper Areas(one on the other side that you cannot see in this image) that are separated by the
Lower Area and the
Structure. The
Lower Area provides a movement obstacle where the
Structure provides a vision obstacle.
Our
Detail sits around and makes everything look pretty.
Back to your build. In this situation we have
Main area3 Upper AreasA stuffload of Random Objects1 or 2 small structuresThe issue? The height difference should almost always be in the
center of the map, while you have it placed in the corners. Random objects should be used carefully while large structures and height differences should cover everything else. For convenience(although not necessary, but will make the height difference areas more used) the height difference areas should be accessible by ramps.
Another issue is that you have several
Mounds but never commit to any real height difference. Because there are no height differences and no large structures in the central area, the central battlefield becomes fairly easy to see through. Because of the maps build, the central area will most likely be the most used.
A quick thing on drawing people to specific areas: players are drawn to weapon locations and health pack locations. Place them where you want the fighting to happen.
Note that this is talking about DMs with rectangular layouts of the "Battlefield" theme. Other cases require different works and this is catering to a specific kind of DM.
Anyways, this has been Rky being too lazy to write a complete guide, but not lazy enough to not give a mini guide.