Broadly speaking, the first half of the OG quant problems are easy and the second half are closer to the level of actual GMAT questions. The only official source of GMAT problems that is closest to the real questions is the GMATPrep test software. The questions that you see in the tests give you a real sense of the GMAT questions. However, you should not rely on those to practice and build concepts. You should use them in the last few weeks after you have finished OG and practiced from other sources.

I recommend that you practice with OG thoroughly paying more attention to the second half of the quant questions and supplement it with other sources listed on the 'Resources' section of the forum.

While the level of Verbal questions is higher in actual GMAT, you would still need to practice first with the OG questions. In the verbal section of OG all questions have the same difficulty level so I recommend that you give all of them equal practice time.

For additional resources you can again refer to 'Resources' section. Additionally I suggest that you read some of the debriefs from the members on the forum who have scored well. This would give you an idea of the best resources to study effectively.

Hope this helps!

thank you!