As a generic answer, you will want to thoroughly read the Private Pilot - Airplane Airman Certification Standards. This document is the benchmark for the skills which you will have to demonstrate to the examiner in order to pass. Read through it and thoroughly review it. If you are concerned that you cannot perform a skill to the standards listed here, talk with your CFI and go up for another practice flight to work on these areas prior to your practical.
First off, as discussed above, make sure that, not only can your perform the skills listed above, but that you can do them in an unconsciously competent manner. They don't have to be perfect, but be able to demonstrate them to an examiner, to the standards listed above, all while being subject to other environmental stressors - radio chatter, examiner small talk/comments, changes in plans, etc. which are adding to your workload and you have to consciously think about.
Find out who the examiner will be and talk with other pilots to get a feel for this person. Is this person fairly easy to work with? Are they spiteful and just search for ways to trip up and fail a student? The practical will be demanding enough without the DPE acting this way and adding to your stress level.
IMSAFE - Illness, Medication, Stress, Alcohol, Fatigue, Eating/Exercise. Make sure that you can meet these guidelines to make you body as physically prepared for the checkride as possible. Make sure you are not ill and take steps eg wash your hands regularly, stay away from sick people, etc for the preceding week or so before the checkride. Make sure you are not on any medications which will interfere with your ability to operate a motor vehicle or serve as PIC. Avoid stressful situations a few days before the checkride and terminate all studying for the practical at least 12 hours before it is scheduled to avoid burnout. Don't drink or take drugs (duh!) before a check ride. Make sure you get plenty of exercise on the week of the checkride.
And on sleep - GET AT LEAST 8 HOURS OF SLEEP THE NIGHT BEFORE THE CHECKRIDE. Do so in a totally dark, silent and cool room. Turn off and abstain from using computers and portable electronics, smartphones, and tablets at least one hour before bedtime; the blue light from the screens really screws up your circadian rhythm and almost guarantees you light and restless sleep - not good. Eliminate any kind of distractions and do not drink caffeinated beverages at least 3-4 hours before bedtime.
Keep an eye on the weather forecast for the day of the flight. Select days which there will be good visibility and light winds. Even if the conditions are VFR, strong winds are likely to make the landings - especially crosswind landings - very treacherous. You don't want to do an otherwise perfect checkride and then bust it when the plane slams down during landing. If the weather just isn't cooperating with the planned day of the checkride, just re-schedule it. This happens a lot in GA and also the DPEs like it as it demonstrates both a consciousness of weather conditions and a refusal to be rushed and carry out a flight in adverse conditions, something that a lot of pilots do which is just asking for trouble.
Get to the airport early and make sure everything is ready to go. Verify the airplane is available and do a pre-flight check (your examiner will ask you to do a second one) to make sure nothing is wrong with the a/c and it is ready to fly. Identify the room where you will be doing the oral exam and make sure it is set up. Set out your FAR/AIM, charts and plotter, E6B, charts, A/FD, scratchpad and pen/pencil on the table and easy to access for the exam and flight planning. Check your flight bag the night before and make sure you have all your needed gear - E6B, headset, etc that you will need for the ride.
That's about all the pointers I can give you, the rest is up to you. Good luck, birdman. Keep the pointy end forward and the dirty side down.