Here are a few things I try to do when working with any game props, not just 3D terrain.
Try it out before you play.
During the game run is no time to be figuring out how things work. Have a dry run to work out any kinks. If you're setting up a map, lay it out beforehand and figure out if you need to make any changes. If you want the fog of war effect, invest in handkerchiefs or a cheap tablecloth or sheet to cover the unexplored parts of the map. handkerchiefs will let you easily reveal a section at a time while keeping the rest of the map hidden.
Don't be afraid to change things.
If it's not going to work, adapt. If the trigger on your replica blaster won't budge, make allowances for that in your game. Written maps typically have paper-thin walls. You can get away with using dominoes or even folded paper in some cases, but if you're using something unyielding like Dwarven Forge terrain that just won't let you get rooms close enough to fit the map as written, expanding hallways by a bit to get everything to fit together nicely will save you some sanity.
Model specific features first, then modify generic features.
If you have an element which requires a specific layout, model it first and make changes around that element. If your prop blaster needs to have a working trigger, make sure that works first before the rest of the prop makes it impossible to get to the trigger. If you have a trap that needs a hallway to be exactly 80' for whatever reason, lay that part of the map out first and fudge everything else by 5 or 10 feet as needed. In general, start with specific features and allow yourself more flexibility as features become more generic. You'll want to fudge "a 20' hallway" before you fudge "The Orc King Wulgulash's Throne Room".
Simple trumps complex.
If you have a choice on what to modify, go with the simpler option. You've got enough to worry about when running our game without hacking custom terrain or re-making a prop that just won't work. Use what you have and go from there. Handwave during the game if you need to - your players will understand that you don't have 200' of generic hallway to use nor the space to display it if you scribble 200' on the map between two stubby little hallways. Similarly, if you have a huge cavern and no tiles to use, plain graph paper or a battlemat should do just fine - maybe that section of cavern has a different colored floor for some reason. If you need to rework maps for your terrain pieces, rework as little as possible unless you're inspired and your changes will make the game better somehow.
This principle also applies when buying terrain pieces and props. Sure, the throne room and torture chamber are beautiful and very detailed, but how often will you really use them? Can you model those rooms using simpler elements which you can reuse in other areas? If you go shopping with an eye toward gathering multitasking terrain and props, you'll have a more useful item in your GM toolbox for the same money.