Consult an Attorney
The most important thing to do is consult with an attorney. You will not always need to hire an attorney, but reckless driving is a criminal offense in Idaho. That means if you're convicted, you will have a permanent criminal conviction. Consulting an attorney will at least provide you with an idea of what you're faced with.
It is also helpful to look up your driving record. in Idaho you can do this online at the DOT website http://itd.idaho.gov/. Many people are surprised to see what is and what's not on their record. In any event, it's always helpful to at least know what your record looks like.
Getting the speedometer in your car tested can be an important defense to reckless driving. If you believe that your speedometer is not 100% accurate, you can get it tested to confirm whether it's showing the correct speed.
If you're charged with reckless driving, taking a driving course can help you at sentencing. But you should consult an attorney before you take the course. Some courses are online and some courses are classroom courses. An attorney will be able to tell you if taking a course is a good idea and which courses are accepted by your court.
Preparing for your reckless driving case is important, but you should not go at it alone. At the very least you should consult an attorney. An attorney can give you specific advise about your judge and what things the judge likes to see before court. Each county in Idaho can be different.