I agree with everything Rich has said.
One thing to watch out for since you're not a native American English speaker, is that this might prove to be more challenging and not as straightforward as you'd imagine.
Once you take that CAT exam from GMAC, use this as a template to understand your performance, and go through your answers, Put them in a chart of sorts, and first
IDentify the question type.
Identify how you answered, ie. Quan question #,- Geometry - Data Sufficency - Right Triangles. etc. Do this for all sections and types, especially for the questions you answered incorrectly.
THEN see if you can analyze your performance by including these indentifiers:
- 1) knew how to do - got it right
2) knew how to do - got it wrong (careless mistake or something serious missing/though you knew but you didn't)
3) kinda knew but guessed - got it right
4) kinda knew but guessed - got it wrong
5) WTF - guessed - got it right
6) WTF - guessed - got it wrong
7) took too long
8) went too fast
9) went just right
10) Was nervous/triggered by question (and how)
There are a lot of resources available and you want to embody a streamlined effective program because as an applicant, your GMAT will make sure you don't get flagged, but it won't likely gain you admittance everywhere/anywhere. It's how you SHINE as an applicant!
For GMAT study, you need to understand what you know/don't know, then address highest yield topics then work through to the less important ones. Based on WHAT you're getting incorrect, and how, would drive how to start studying. Hands down, studying concepts comes first, then practice, then quizzing, then diagnostic exams. Lather, Rinse, Repeat....
Do NOT go directly to practice questions...you need to create a kind of muscle memory before you play the game. It's the same reason people learn and master scales and chords before learning to play and read complicated music.
Keep us posted, and feel free to reach out to me directly with any questions.