Look for your state Department of Motor Vehicles, better known as the DMV. Sometimes the DMV is its own entity, while other times it operates under the Department of Public Safety in your state.
Ask your state DMV about practice tests. The reason you must go through your particular state is that traffic laws and driver's tests vary from state to state. One state may allow for turning right on red after a stop, while others don't.
See if your state DMV has a website. Most state government offices do. Driver's manuals for a regular license, motorcycle or commercial license are often posted online and may include practice tests.
Enroll in an accredited driving school. Accredited schools work closely with state offices that issue driver's licenses. Furthermore, driving schools are businesses that want to see you do well because it reflects on them. A driver's education course through school or a private driving school is often required for drivers under 18.