High School Diploma
Most truck driving schools will require you to have a high school diploma or its equivalent, a GED. If you do not have either of the two, you will most likely not be getting admission in the school. Make sure that you get a GED if you had dropped out of high school.
The minimum age to join a truck driving school is 18. If you apply before the age, there will be no use as your application will be turned down on the basis of you being too young. So wait until your 18th birthday before you apply.
Be Physically Fit
Make sure that you are in good shape when you apply. You will likely have to go through a fitness test that is prescribed by the school and you must pass it to get in. It is generally the DOT approved physical exam that a doctor administers. If you are in a bad shape, do some workouts to get physically fit.
Clean Driving Record
Having a clean driving record is important as you want to present yourself as a candidate that is serious about driving. If you have too many tickets on your drivers license, your case for the admission will be weak and you may be denied an admission.
You must be drug free when you apply as it is one of the requirements for joining these schools. They do get a drug screening done for candidates and if you have drugs in your system, applying to the school will be a waste of time. It will also affect your chances of getting in to one in the future as well.