Tips for the private pilot check ride
Do NOT worry about getting an unsatisfactory result!!  It just does not matter.  There will be no record of it anywhere but in your memory.  It's not noted on your certificate and, really, nobody will care.  The PPL is a license to learn and that is what you'll be expected to do after you pass.  The checkride merely assesses basic requirements.  Now, if you want to be a professional pilot...it still doesn't matter.  Nobody will care if you made a dumb mistake on a PPL ride and had to go back and demonstrate a maneuver again.  Anyone who does is not worth working for anyway!

Think about it, worst case you have to go flying again (that's a pretty good "worst case").  The only downside I see is having to pay the examiner fee again.

Ok, but real advice...
1.) Get sleep the night before.  You'll be nervous, but sleep anyway.  You already know everything you need to know to pass, a few more hours of studying won't make or break the ride.

2.) It's ok to say "I don't know the answer, but I know where to find it," and then look it up.  You can't say it for every answer, but it's not a deal breaker to not know something.

3.) At least one experienced pilot (your CFI) thinks you're ready to be a PPL.  If you took a stage check with an evaluators at a flight school, two experienced pilots think you've got what it takes.  CFIs don't sign off on a checkride if they think the student will fail.

4.) Be able to explain why the plane is legal to fly.  One of the examiners I used loved to ask the students to prove that the plane was legal.

5.) Be able to explain why you're qualified to take the exam.  The same examiner would routinely ask students to prove that they were qualified to take the exam.

The only way this ends is with you earning a PPL.  If it takes two rides, so what?  You've already done the hard work.  Just go flying with the examiner and show him/her what you've been showing your instructor for the past few hours.

Good luck.  Don't sweat it.