Well of course it all depends on the type and levels of the extraneous noise youre fighting. Clearly using a directional mic pointing away from the noise will help, but if the noise is audible in the space youre pointing into then the mic will hear it as the sound is reflected not only direct.
what are the surfaces like in the space. Soft and absorbent or hard and reflective. Parallel to one another or broken up by screens and soft furnishings etc, carpeted or hard floor,
Is the ceiling low and absorbent or high and hard.
Why cant you do anything to isolate the space if this is given for you to shoot in?
You really want the walls to be solid and dense enough to stop sound transferring into the shoot space from outside. I suggest building a brick cavity wall filled with dry sand, and then treating the inside surfaces with absorbent panels to deaden the interior space.
It all depends on how serious you are about getting it to sound good.
Peter
Post Production Dubbing Mixer