Hi Khalid689,
There's certainly no harm in studying for the GMAT for the purposes of honing your general critical-thinking skills, but depending on the specific skills that you're looking to work on, you might find that studying for the LSAT might be more appropriate. Can you go into more detail about how you're specifically looking to enhance your skills?
If you do choose to study for the GMAT, then to start, it would be a good idea to take a FULL-LENGTH practice CAT Test; you can take 2 for free at
www.mba.com (and they come with some additional practice materials). If you want to do a little studying first, so that you can familiarize yourself with the basic content and question types, then that's okay - but you shouldn't wait too long to take that initial CAT. That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can discuss how you might best approach your studies.
GMAT assassins aren't born, they're made,
Rich