There are lots of ways to be unsuccessful on a practical test because there is a lot to accomplish and all of it to fairly high standards. Some of the errors follow predictable, repeatable patterns that I will try to point out here at each level of experience. Frequently, none of these lapses are reasons for immediate failure in and of themselves, they just make your whole job more difficult! If any task is unsuccessful, the entire test is unsuccessful and this whole "area of operation" must be retested. You do however, get credit for everything you performed to the standards So in a way, the dreaded "pink slip" is a really a credit slip for everything that went right because without it on a re-test, you would have to fly an entire test again.
For starters, let's describe how any test should go when everything is working correctly. To perform your best on any evaluation, arrive on time, well-rested and properly nourished. Make sure you allow enough time to prepare so you do not feel compelled to stay up all night cramming and organizing. To achieve this goal utilize some pilot skills: make a check list for items to accomplish ahead of time and items to bring to the test. This whole category could be subsumed under the advice: don't rush and organize carefully. You will be more calm and confident!
Since we need to assure the plane is airworthy before we fly a test, we need all the maintenance records required to prove this and a working knowledge of the different inspections. Similarly, you as pilot in command will need all your personal documents and experience records (log and endorsements) to prove that you are qualified to be PIC and to take the flight test you intend to take. Bring your flight planning tools, headsets and all your pilot paraphernalia. Current charts and a FAR/AIM would also be essential to have along. Remember, on the oral your documents are resources that you can consult! Please sit down with your CFI and review your paperwork for the evaluation, all your experience and endorsements so there are no "surprises" that prevent us from testing.
In the aircraft and during the flight, using the checklist carefully will prevent rushing and keep you organized. Clear the area carefully and deliberately before every maneuver and keep a look out throughout the test. This is one of the "emphasis items" you can find in the preface of every Practical Test Standard (along with many other essential tips). Clearing also gives you more time so you don't feel rushed. Prompt correction of any deviations is essential and wins big points with any examiner. We are watching carefully and especially value pilot-in-command authority which is demonstrated by handling the plane precisely. (Just because you have plus and minus 100 feet does not mean you have to use all of it!)