See, Don't target for 85+ marks.You may find in mechanical engineering 100 students more than 85.You have exact 3 months for preparation. If you use it wisely you 'll definitely get a good score. You being civilian must focus on some important core subjects like geotechnical, environment, transportation along with structures. Maths and aptitude round up for 30 marks. Just don't read each and everything. Go for understanding concept and solve as many new problems as you can. This is a numerical oriented exam. Practice a subject and revise it more number of times. Revision is must. Don't read anything new before exam. Whatever you have read revise it at least 4 to 5 times. Join ace or made easy test series. Its must, you will know where you stand and rectify and correct your mistakes. And till the exam don't lose motivation. Many people give up just before exam. It will be better if you follow any class notes. You have less time so it will give you proper guidance. Good Luck!!!