Selecting a bicycle route can bring joy to a ride or make it miserable. Debbie and I have experienced this first-hand - the good, the bad, and the dangerous.
It's easier to vet routes and avoid bad ones before you embark. Bicycle shops, Internet message boards, pre-printed bicycle maps or GPS downloads, and websites such as ride by GPS can help keep you out of harm's way and send you on pleasurable, low-trafficked roads with beautiful vistas and ample sight lines. Even Google Maps knows bicycle routes.
If you're planning a tour, check out Adventure Cycling Association and its interactive route maps across the United States.
If you're already on a difficult route - perhaps dealing with road construction, poor pavement quality, or heavy traffic - it's hard to undo those consequences. Talk beforehand to people who have ridden those routes. Drive them. Or call a local bike shop and ask them about the route you're considering. A little due diligence can go a long way to improving your riding experience.
Sometimes, the worst source of information is local people who aren't bicyclists. Though often eager to help, they can't seem to translate driving a car to riding a bike. Some of them think any road is dangerous on a bicycle.
We've had people recommend roads that we later regretted taking. Narrow or nonexistent shoulders, rumble strips (how were they to know?), bad pavement, excessive or high-speed traffic - you name it - you can't count on locals for advice unless they have ridden a bicycle over those same roads.
In the absence of better information, we'll still consult locals. But we're skeptical and ask questions to clarify what we're getting.