GMAT Strategy

hi,
After understanding the basic concepts of cr, i started og 12 cr. Now i finished about 80 of total 124. My correct rate is only 65%. Very disappointing.
Also I bought CR bible, i find the book is too heavy to read it all.
During the exercise of CR. i notice once i can fully understand the sentence and its question, i will choose the right answer most of time. But if i dont get the meaning of the sentence well, i fail. More, now i probably spend 2-2:30 mins on each CR. too long!
I know, for a beginner, be patient and practice more.
But could anyone offer some effective approaches or tips, etc?
Some people say different types of cr questions may have different solving skills. Some people can eliminate wrong choices immediately. How can we achieve these and where can we find useful study material.

Many thanks in advance.

btw, how is mgmat cr prep? better than power score? Any comments?