Read the books, then do a test exam from the confuser.
Read the books, do another until you can consistently get a pass.
It's useful to photocopy the answer sheets so that you can do several tests - it's also useful to compare tests to see what you are consistently getting wrong, and revise that specifically before taking the actual paper.
Don't confine your reading to just the Thom or Pratt books - read magazines, CAA safety sense leaflets, books on aviation - they all increase your knowledge and (possibly) wisdom and help to pass the exams. Presumably, as you are training to be a pilot, you enjoy reading about aviation, so this is a pleasure, not a pain!
You don't have to spend whole days or nights studying - as Evo says, a half-hour regularly adds up. You've got 18 months to do them in...
Good luck.
SD