Start well in advance. The tests are taken in the spring, so begin by February at the latest.
Set up a schedule. If you are going to work on TAKS preparation for 30 minutes each day, mark it on the family calendar and then tick it off when it is done. This creates a record of how much study was completed.
Download the latest tests. The tests are released only every three years, to keep down the number of new questions needed. Even though questions from previous years won't be the exact wording, they will give you and your son a very good indication of what to expect.
Learn about computer tests by writing the TAKS yourself. This will give you a better idea about what it is like to take this multichoice exam. To develop more empathy, imagine that you are writing it when you are the age your son is now.
Check the "teacher" sections of TAKS preparation sites to see what they advise. This will help to get you thinking more like a tutor and less like a parent.
Keep a record of the results of each test your son writes. Identify areas where he needs additional help. For instance, his math skills might be very good, but he could be weak in English and needing remedial work in that area.
Print a hard copy of the tests. Sit down with your son and have him read the questions to you, and then mark the answer he thinks is right. This is an opportunity for you to assess how well he is doing.
Be encouraging and supportive. Even if you have some concern about how well he will fare on the tests, stick to the positive. The best result will come from your son thinking he is going to do well on the TAKS.