I figure any location worth making a set is worth gang setting. I personally make at least three sets at each prime location. These locations can be intersecting fence rows, crop change areas, a weed strip left in the middle of a crop field, and natural draw stations such as a deer carcass or the spot of a previous catch.
On how close to set the traps apart gang setting can range from a few feet to 20 yards or more. I'm sure each trapper has his/her own opinions on the subject...I'm just telling you what has worked for me.
One of my favorite gang sets is to make three new sets off the edge of a catch "circle". If you can envision the torn up area from a catch as a clock...I personally will make three new sets at six, ten, and two o'clock off the edge of the circle.
This set can and has yielded me triples on fox on more than one occasion. It does not always work as intended as on one occasion I caught a Gray Fox, an oppossum, and a Turkey in the same circle set...on the same night...I know Turkeys are not nocturnal...I've still never figured that one out.
Oh yes...make sure your trap chains are short enough to keep your catches from tangleing with each other...hope this helps.