It's a good idea to know the broad ranges of normal for labs values so that if one is given, you can quickly bypass the normal ones and concentrate on the abnormal one.
Then when looking up the reference charts, you will only have a confirm that it is abnormal. It'll save you a lot of time.
The one problem with shelfs for me have been having a enough time to finish all the questions because the questions can be so long. So learning how to read through questions quickly and focus in on the problem can be a lifesaver.