For many of you, the first obstacle you will face in physics graduate school is the written qualifiers. The qualifiers can be quite different for different programs but there are many similarities.
My first bit of advice is to seek out good preparation material. Most schools will give you samples of their old exams so you want to be sure you get as many of these as are available. Other schools provide sample problems as well and perhaps their sample problems will be excellent preparation material for your exam. You might find the following Google custom search tool helpful as I defined the search index to include only physics department websites that offer graduate physics programs. For example you might try searching for "qualifiers":
My second bit of advice has to do with taking advantage of your first opportunity to pass one or more of the qualifier exams. When I went to graduate school at UCSC they gave the incoming graduate students the written qualifier exams before we even learned anything. Although many people downplayed the significance of the first attempt for the incoming class, it was very clear then the returning students didn't downplay the significance of their second attempts. The way my program worked is there were 5 subject areas E&M, Quantum, Classical, Mathematical, and Statistical. If you happened to pass one or more of the exams they you didn't have to take that particular exam the following year. The level of stress for the returning students who had to pass 4 or 5 of the exams was very different from the level of stress from returning students who only had to pass 2 or 3.
Hopefully other people will contribute their opinions and this thread will grow into a great resource to help graduate students prepare for their qualifier exams.