Try to get a normal night's sleep before you leave. Do not leave on a trip if you are already tired. Plan your trips so you can leave when you are rested. Do not take any medicine that can make you drowsy. Do not eat a large meal before you leave.
Some people get sleepy after they eat a big meal.
Stop every hour or so or when you need to. Walk around, get some fresh air and have some coffee, soda or juice. The few minutes spent on a rest break can save your life. Plan for plenty of time to complete your trip safely. Try not to drive late at night when you are normally asleep.