Hello gaurav.......it is good to know that at least you know your problem that is "you are unable to sort out your strength and weakness"....but i think this is one of your strength that you are trying to solve your problems that is positive attitude.
Now here are few methods which may help you...

(1) you can take a pen and a piece of paper sit at your room ,divide the page in two half and honestly like a neutral or third person try to write your strengths and weakness in two columns .Here the most important thing is that " You write on that paper like you are writing strengths and weakness of some other person with honesty because in my opinion "you are the only person who knows much more about yourself then others".While writing you can think of some incidences that took place when you showed your strengths and weakness.After writing them down put that paper aside and after few hours again look at that paper if you feel like writing more then write or otherwise read it carefully as someone else has written for you and probably you will find the solution.Then try to improve on your weakness. Here the keyword is "write honestly" otherwise whole practice will be of no use.
(2)If you are unable to do it by yourself then there is another way.....in your daily life you meet with lot's of people ,you make some friends also. Try to select some friends or relatives which have neutral or positive attitude (do not select people who will just try to make you happy by saying good things about you )and ask them to tell your strength and weakness and note it down and after consulting with all of them .Go to your place and sit in a stable environment and then read that paper. After reading it i think you may get most of the solutions.The key word here is "selection of neutral people".
Finally i want to say do not get frustrated because i can tell that there are very few people who know there problem and try to solve them .Most of them neglect it.But you are trying to solve and trying to find solution this is positive think ,keep it up and do not get frustrated.My best wishes are with you