The main thing is this......
You are as safe as you make yourself become. Getting a CDL through a mill will get you behind the wheel, its up to you to make sure you have the training/knowledge to be there safely. Anytime you question something, ASK ASK ASK!!! Someones life may depend on it! Hanging out in the evening at the counter of your local truckstop is a good place to get knowledge. After spending the day driving in their truck, yacking for a few hours over a cup of coffee appeals to lots of drivers because they are bored. Most are very proud of their work and are more than happy to impart info.