When it comes to the oral...
Keep your answers simple and to the point. For example, if they ask you the battery voltage, don't describe the entire electrical system, just tell them the battery voltage. If they want you to describe the electrical system they'll ask you to. Don't tell him/her "more than you know", because it will be readily apparent and give them a reason to start probing you. As I said, if they want more detail, they will ask you for it. If you are asked a question that you don't know, don't panic - simply say you don't know the answer. (Hopefully, it won't be in an area that you really ought to know and understand.) Many examiners will ask questions like that to see if you know where and how to look up the kind of stuff that you aren't going to remember out in the real world.
Don't sweat the checkride too much. (Sure, that's easy for me to say.) Just remember that, to one degree or another, your CFI is also on the line here (The FAA gets interested in CFI's with low pass/fail ratios.) and he/she isn't going to recommend you until they are 100% satisfied that you're ready. When I'm prepping a student for a checkride, my oral and final training flight with the student is MUCH more difficult than anything an examiner will require. Most examiners have the point of view that all they are looking for is to verify the instructor's recommendation that you are ready for the license. They're not looking for perfection - no one has ever flown a perfect flight - just safety and compliance with the requirements. Have fun and be sure to let us know how it goes.
'Sled
