You have to gather a bit study material, mock CAT papers and practice test papers in order to prepare in one month. You can easily search and find free and paid mock test online. You just need to look for genuine and reputed sites in order to get them. You have to pay some bucks for paid mock tests but this is worth buying. You have to focus on basics and strengthen it. You can choose best books like Arun Sharma in order to clear the basic concepts. You should also look for the books come with short tricks, tips and shortcuts that you can put together in brief.
You can develop your technique to deal with LR and DI as there is almost no theory. You should have good command over verbal English portion that is very tricky ground. You have to work on grammar basics and polish up vocabulary. You just need four weeks to get ready for the exam.
You can start with solving mock CAT paper that you get from online tests or hard copy. You have to solve these papers every day. You have to solve 6 mock tests by the end of the first week. You have to look at the solutions for every question after solving every mock test. It is called concept building. You have to finish at least 2 maths topics everyday along with lots of practice problems. You should practice two problem sets every day from verbal section.
You should go for the concept strengthens exercises during 2nd week. You should read books, newspaper, magazines on any topic. You have to start working on LR and DI and attempt one mock test each day. You can also find the question types that repeatedly occur so that you can predict the exam pattern. You will get an idea about the questions which are difficult to solve and which are more scoring. It helps formulate test taking strategy.
Once you come across the high scoring questions, you will find your strength. You have to work on these questions. If you find any question type which is difficult to manage, you can skip them if they constitute less than 10% of the total marks.
You have to figure out the topics and concepts that are used more and more like counting, number system and much more. You have to practice and strengthen these topics and concepts as well.
You may feel the shortage of time during 3rd week but you need not to worry about. You need not to work on new topics and concepts. You have to remember and revise whatever you have read and learnt in last 2 weeks. You have to revise formulae and don’t forget the techniques you worked on. You need to practice only on high priority topics. You have to work on few sectional tests as well as this would be speed building activity. More sectional tests should be solved during 3rd week. You need to work on mistakes you have been making so far. You have to go with full length mock test during 4th week. This is how you can plan preparation for CAT in one month.