For DILR preparation you need to keep practicing the lengthier method of solving the question. Using the right approach is must if you want to get prepare for DILR.
The following steps you can apply:
1.Get to know the types of questions (topics) of DILR.
2.Grasp the tricks used in each type.
3.Build a mental legend for the nomenclatures/symbols used.
4.Develop the ability to decode the constraint in action.

CAT is a national level MBA entrance exam so we can definately say that CAT is one of the toughest exams to crack. But if you prepare yourself in a proper manner and in a right way any average student can crack CAT. Unfortunately most students who prepare for CAT do so in a faulty manner.
Galvanizing Potential gives you a proper guidance and tricks to crack CAT.

Here are some thoughts on a good section approach:
1. Take a few minutes to analyze the assignment and make a strategy about how you are going to solve this section.
2. Don't ask any questions! This is a serious mistake and can cost you dearly. Try to maximize your efforts. See why 90-100% accuracy is difficult to achieve, so maximize your efforts and improve your score.
3. If you get bored while reading RC, try to adapt your approach. For example, try to do 1 RC first and then solve some VA questions and then go back to RC and so on, to neutralize.
4. Focus on what the author wants to say, not what he wants to explain. Keep solving the exercises and analyzing them. This will help you to plan your strategy in advance.

IIM is the top MBA institution in India, for admission in these kind of reputed institute you must follow the admissionn rules and eligibility criteria. There is no such rule by which you can admission directly into an IIM.
The best and only way to get admission into IIM is by clearing CAT.