Stability
Use triangular structures for increased stability.
The middle of a bridge usually is the area that needs the most support.
Always attach cables to supports, such as concrete archways.
Various General Tips
You should always use a basic triangle pattern for building your bridges.
While the bridges basic building unit should be triangles, the overall look of the bridges should be oval, to better distribute the weight.
There are three secret achievements in Bridge Constructor: Stubborn (25 failed simulations in a row for the same bridge), Smart Alec (if you don't build the 1st level to specification), and Safe Flight (ran a simulation even though you didn't place a single element), all of which are worth 10 points.
