I struggled to improve my score just from book review. So I'm now using a combination of approaches. This includes an online GMAT prep course, it's iPhone app, a private tutor which goes through the difffcult questions i can't get right and some apps which help me with my basic and mental maths. This new approach has paid off and my GMAT score has increased nicely in practice tests.Magoosh
has some study plans which might help.
Good luckPosted from my mobile device