It is recommended that all the GMAT aspirants start their preparation with the OG.Start with the quant section and work out the problems given in the OG.The same should be repeated for the verbal section.Typically you may need 2 weeks to complete all the problems given in the OG.Do remember that the problems in the OG are relatively easy when compared to those from other sources..After you are done with OG,start with Kaplan and work out all the problems in it.Download GMAT flashcards and Spideys notes from the resources section in this forum.It will definitely help you to enhance your scoring skills..

If time permits you can also work out the GMAT tough problems,which can be found in the resources section..You can work out a set (usually of 25 questions each) of problems in each section(CR,PS,DS,SC & RC) daily and time yourself..As far as DS is concerned the only way to master them is to go through the posts written by experts in this forum..Even I was very weak in the DS section.You can search for experts like Ian Stewart,Stuart kovinsky in this forum and go through all the posts written by them.It will definitely help you a lot..Best of luck for your preparation