about a fortnight before the date scheduled for the exam make sure you have downloaded the objectives from comptia's website.
concentrate on practise exams, be they free or otherwise.
www.certify.com www.examdrill.com
print off the objectives and mark the ones that you continually score poorly. study those and take more practise exams. continue to mark down what you score poorly and retake practise exams and you will find that your scores will improve.
average scores of 75%+ will show readiness, but aim for 85%+.