If you find specific fish holding at one particular depth on one piling, odds are very good that the next piling you move too will have fish holding at that depth there as well. Depending on what type of bridge you are fishing, you can generally find an abundance of rip rap on one or both sides. Rip rap draws smaller baitfish into a generel area as well and combined, offer aspects that make bridge fishing hard to beat. Live bait rigs and jig and minnow combos are almost always effective if you can make the most of your presentations. This genereally requires a depthfinder and a big enough lead hea to get the job done which in turn is dependant upon current.
Experimentation is the key.