MBA exam or CAT preparation depends on when you the start preparation, current level of expertise and other commitments apart from test preparation.
 
Typically, most candidates would plan the following steps in their MBA preparation:

• Learn core concepts in numeric & verbal ability.
• Practice sample questions.
• Attempt mock test.
• Work on weaker areas.

As a thumb rule, preparation should be structured in a way to consolidate performance in the strong sections, while eliminating weakness in the other areas.
 
It is often the weak areas that provide maximum opportunity to improve performance. Based on your core skills, form a strategy to develop complete expertise. For instance, if verbal reasoning is the weaker area- make a conscious effort to improve through extensive reading on varied topics. On the other hand, those fearing maths would benefit from starting with a high school book to learn algebra, commercial maths, geometry and trigonometry.
 
Another focus area in early days is keeping abreast with current events in the economy, politics and corporate sector. This can prove handy in the group discussion & Exam stage. Think of relevant topics and organize mock discussion sessions with your peers.